全文获取类型
收费全文 | 891篇 |
免费 | 70篇 |
国内免费 | 1篇 |
出版年
2022年 | 7篇 |
2021年 | 15篇 |
2019年 | 12篇 |
2018年 | 17篇 |
2017年 | 9篇 |
2016年 | 10篇 |
2015年 | 23篇 |
2014年 | 31篇 |
2013年 | 34篇 |
2012年 | 65篇 |
2011年 | 35篇 |
2010年 | 29篇 |
2009年 | 37篇 |
2008年 | 36篇 |
2007年 | 49篇 |
2006年 | 40篇 |
2005年 | 46篇 |
2004年 | 34篇 |
2003年 | 51篇 |
2002年 | 42篇 |
2001年 | 13篇 |
2000年 | 12篇 |
1999年 | 21篇 |
1998年 | 12篇 |
1997年 | 9篇 |
1996年 | 8篇 |
1995年 | 6篇 |
1994年 | 13篇 |
1992年 | 12篇 |
1991年 | 12篇 |
1990年 | 9篇 |
1989年 | 12篇 |
1988年 | 8篇 |
1987年 | 10篇 |
1986年 | 9篇 |
1985年 | 13篇 |
1984年 | 16篇 |
1983年 | 9篇 |
1980年 | 9篇 |
1979年 | 7篇 |
1977年 | 10篇 |
1975年 | 7篇 |
1973年 | 10篇 |
1972年 | 5篇 |
1971年 | 14篇 |
1970年 | 9篇 |
1969年 | 12篇 |
1968年 | 6篇 |
1967年 | 5篇 |
1966年 | 6篇 |
排序方式: 共有962条查询结果,搜索用时 46 毫秒
41.
Negative correlations between clutch size and population density are proposed to be considered as indices of intra- and interspecific competition in cladocerans if they are revealed while analyzing population dynamics and clutch size and time lags are taken into account. The proper correlation analysis of summer populations of Diaphanosoma brachyurum, Bosmina coregoni, Daphnia cucullata and D. galeata from mesotrophic Lake Glubokoye (Moscow Region) in 1975, 1978, and 1979 indicates the important role of competition of both types for the community studied. High niche overlap in food and space in the four populations was also observed. 相似文献
42.
V V Matveev 《Tsitologiia》1984,26(4):438-443
Tumor actomysion preparations isolated by three different extracting solutions are very similar in composition. A characteristic feature of the preparations obtained is a very rapid presumably proteolytic degradation of their components. It is shown that the major polypeptides of freshly prepared samples are not products of proteolysis. The major protein components of these preparations are identified. 相似文献
43.
Stable genetic transformation of white pine (Pinus strobus L.) after cocultivation of embryogenic tissues with Agrobacterium tumefaciens 总被引:4,自引:1,他引:3
Levée V. Garin E. Klimaszewska K. Séguin A. 《Molecular breeding : new strategies in plant improvement》1999,5(5):429-440
A genetic transformation procedure for white pine has been developed after cocultivation of embryogenic tissues with Agrobacterium tumefaciens. This efficient transformation procedure led to an average of four independent transformed lines per gram of cocultivated embryogenic tissue and up to 50 transformed lines can be obtained in a routine experiment. Constructs bearing the uidA gene or the green fluorescent protein (GFP) gene were introduced and -glucuronidase (GUS) activity was followed over time. The expression of the uidA gene was lowest with a 35S-gus-intron construct and was 20-fold higher with a 35S-35S-AMVgus::nptII construct. The addition of scaffold attachment region (SAR) sequences surrounding the gus::nptII fusion did not significantly enhance the GUS activity. Transformed mature somatic embryos have been germinated and plantlets are presently being acclimatized. 相似文献
44.
The oral dentition and type and number of taste buds (TB) on the lips and in the oropharyngeal cavity were compared by means of SEM in 11 species of cardinal fishes (Apogonidae) belonging to five genera. The occurrence of a dense cover of skin papillae on the lips of some species (e.g., Apogon frenatus), as well as differences in structure of vomer, tongue, and palatinum, expose additional morphological characters important for clarification of the taxonomy of this group of fishes. Differences are also revealed in the type of dentition, such as on the vomer and epi-hypopharyngeal bones. Strong and dense dentition of the anterior part of the oral cavity and a high number of TB on this site in species feeding on larger prey (e.g., Cheilodipterus spp) is compared to the relatively feeble jaw armor and richness of TB on the more pharyngeal site in species feeding on smaller prey (e.g., Apogon angustatus, A. frenatus). In addition to the three types of TB (Types I-III) previously described from various teleost fish, a fourth type (Type IV), comprising very small buds, was found in some cardinal fish (Apogon angustatus, A. frenatus). The various TB are distributed from the lips to the pharyngeal bones, on the breathing valves, tongue, palatinum, and pharyngeal bones; their number and type on the various sites differ in the different species. In all species studied the Types I and II TB, elevated above the surrounding epithelium, dominated the lips and anterior part of mouth, while Types III and IV, which end apically at the level with the epithelium, dominated the more posterior pharyngeal region. The highest number of TB, around 24,600, were found in Fowleria variegata, a typical nocturnal species, and the lowest in the diurnal and crepuscular Apogon cyanosoma (1,660) and Cheilodipterus quinquestriatus (2,400). Differences are also revealed in the type of dentition, such as on the vomer and epi-hypopharyngeal bones. The number of TB increased with growth of the fishes. The differences in the total number of TB and their distribution in the oropharyngeal cavity in the various species indicates possible different mechanisms of foraging and food-recognition. 相似文献
45.
Nitzan D Kronenberg J Horowitz Z Wolf M Bedrin L Chaushu G Talmi YP 《Plastic and reconstructive surgery》2004,114(5):1060-1067
Parotidectomy is performed for benign or malignant tumors and for selected benign inflammatory and autoimmune conditions. Possible associated complications include facial nerve paralysis, pain, loss of sensation, gustatory sweating, and facial scarring. Global quality of life in patients undergoing parotidectomy has not been reported. The implications of facial surgery with the catastrophic potential of facial nerve paralysis may severely affect quality of life. A quality-of-life study was conducted in patients undergoing parotidectomy for benign and malignant diseases to define the significance of associated morbidity and its impact on quality of life. A quality-of-life instrument was specifically created, based on the principles of the University of Washington Quality of Life questionnaire, and mailed to the patients. Questions addressed recognized complications of parotidectomy. Patient group results were compared for age above and below 45 years, sex, benign versus malignant disease, presence or absence of Frey syndrome, and presence or absence of benign pleomorphic adenoma. Forty-six percent of 125 patients meeting the study criteria fully replied to the questionnaire. The global health score was 3.5, corresponding with "good" to "very good." Except for local sensation, which had a score of 50, all other domains scored above 76. Change in appearance, gustatory sweating, and pain were reported by 70 percent, 57 percent, and 30 percent, respectively. Importance attributed to all domains except facial function was low. Pain was encountered significantly less in patients younger than 45 years of age, and scores for appearance were also highly significant in this age group. Postoperative sequelae were noted in the majority of patients. The dominant sequelae were altered sensation, change in appearance, Frey syndrome, and pain. A degree of permanent postoperative facial nerve impairment was reported by 10 patients. Nevertheless, overall, parotidectomy does not seem to severely affect quality of life. 相似文献
46.
Beloussov LV 《Bio Systems》2003,68(2-3):199-212
Any reactions of the living systems are to a great extent context-dependent. Meanwhile, the biological essence of a "context" remains to be obscure. We suggest that it may be based upon an ensemble of molecular-supramolecular oscillators, which have different characteristic times. For testing this hypothesis, we applied the Fourier statistics to the time series of the records of an ultraweak photon emission (UWPE) registered from fish eggs and embryos and from cell cultures. We detected the regular changes of the UWPE Fourier spectra (FS) during embryonic development and physiological reactions of cell cultures. In many cases, such changes were going on in a holistic manner, i.e. involving broad spectral areas rather than single frequency maxims. FS of the earlier developmental stages showed greater instability and the presence of a short-range order only. On the contrary, at the advanced developmental stages a long-range order has emerged within the spectra. Another distinction of the highly organized biological samples (developing embryos, confluent fibroblasts cultures) from non-biological controls and "poorly organized" samples (non-fertilized eggs, non-confluent, poorly spread cell cultures) was the UWPE correlation dynamics which was more cooperative in highly organized samples. A non-invasive technique of UWPE registration may be useful for exploring a fluctuated oscillatory background of the developmental and physiological states of biological samples. 相似文献
47.
Mulligan CJ Robin RW Osier MV Sambuughin N Goldfarb LG Kittles RA Hesselbrock D Goldman D Long JC 《Human genetics》2003,113(4):325-336
Enzymes encoded by two gene families, alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH), mediate alcohol metabolism in humans. Allelic variants have been identified that alter metabolic rates and influence risk for alcoholism. Specifically, ADH1B*47His
(previously ADH2-2) and ALDH2-2 have been shown to confer protection against alcoholism, presumably through accumulation of acetaldehyde in the blood and a resultant 'flushing response' to alcohol consumption. In the current study, variants at ADH1B
(previously ADH2), ADH1C (previously ADH3), and
ALDH2 were assayed in DNA extracts from participants belonging to a Southwest American Indian tribe (n=490) with a high prevalence of alcoholism. Each subject underwent a clinical interview for diagnosis of alcohol dependence, as well as evaluation of intermediate phenotypes such as binge drinking and flushing response to alcohol consumption. Detailed haplotypes were constructed and tested against alcohol dependence and related intermediate phenotypes using both association and linkage analysis. ADH and ALDH variants were also assayed in three Asian and one African population (no clinical data) in order to provide an evolutionary context for the haplotype data. Both linkage and association analysis identified several ADH1C alleles and a neighboring microsatellite marker that affected risk of alcohol dependence and were also related to binge drinking. These data strengthen the support for
ADH as a candidate locus for alcohol dependence and suggest further productive study. 相似文献
48.
Hill BC Becker L Anand V Kusmierczyk A Marcovina SM Rahman MN Gabel BR Jia Z Boffa MB Koschinsky ML 《Archives of biochemistry and biophysics》2003,412(2):186-195
Low-density lipoprotein (LDL) oxidation is stimulated by copper. Addition of a recombinant form of apolipoprotein(a) (apo(a); the distinguishing protein component of lipoprotein(a)) containing 17 plasminogen kringle IV-like domains (17K r-apo(a)) protects LDL against oxidation by copper. Protection is specific to apo(a) and is not achieved by plasminogen or serum albumin. When Cu(2+) is added to 17K r-apo(a), its intrinsic fluorescence is quenched in a concentration-dependent and saturable manner. Quenching is unchanged whether performed aerobically or anaerobically and is reversible by ethylenediaminetetraacetate, suggesting that it is due to equilibrium binding of Cu(2+) and not to oxidative destruction of tryptophan residues. The fluorescence change exhibits a sigmoid dependence on copper concentration, and time courses of quenching are complex. At copper concentrations below 10 microM there is little quenching, whereas above 10 microM quenching proceeds immediately as a double-exponential decay. The affinity and kinetics of copper binding to 17K r-apo(a) are diminished in the presence of the lysine analogue epsilon -aminocaproic acid. We propose that copper binding to the kringle domains of 17K is mediated by a His-X-His sequence that is located about 5A from the closest tryptophan residue of the lysine binding pocket. Copper binding may account for the natural resistance to copper-mediated oxidation of lipoprotein(a) relative to LDL that has been previously reported and for the protection afforded by apo(a) from copper-mediated oxidation of LDL that we describe in the present study. 相似文献
49.
Fedorov Lev M. Tyrsin Oleg Yu. Krenn Veit Chernigovskaya Elena V. Rapp Ulf R. 《Transgenic research》2001,10(3):247-258
The ability to control gene expression in a temporal and spatial manner provides a new tool for the study of mammalian gene function particularly during development and oncogenesis. In this study the suitability of the tet-system for investigating embryogenesis was tested in detail. The tTA
CMV
(M1) and rTA
CMV-3 (reverse Tc-controlled transactivator) transgenic mice were bred with NZL-2 bi-reporter mice containing the vector with a tTA/rTA responsive bidirectional promoter that allows simultaneous regulation of expression of two reporter genes encoding luciferase and -galactosidase. In both cases reporter genes were found to be expressed in a wide spectrum of tissues of double transgenic embryos and adult mice. The earliest expression was detected in tTA
CMV
(M1)/NZL-2 embryos at embryonic day 10.5 (E10.5) and rTA
CMV
-3/NZL-2 embryos at E13.5. Doxycycline abolished -gal expression in tTA
CMV
(M1)/NZL-2 but induced it in rTA
CMV
-3/NZL-2 embryos including late stages of embryogenesis. The tTA and rtTA transactivators thus revealed a partially complementary mode of action during second half of embryonic development. These experiments demonstrated that both Tet regulatory systems function during embryonic development. We conclude that the Tet systems allows regulation of gene expression during embryonic development and that double reporter animals like the NZL-2 mice are useful tools for the characterization of newly generated tet transactivator lines expressing tTA (or rtTA) in embryonic as well as in adult tissues. 相似文献
50.
Previously, we found no segregation in F2 obtained from crosses between two Dileptus anser clones differing (under the same culture conditions) in their serotypes, i.e. in their immobilization antigens (i-antigens); indeed, all the F2 clones had mixed, i.e. hybrid serotype, being immobilized simultaneously with both immune sera developed against either parental clone (Uspenskaya, Yudin, 2000). Presently, experiments were carried out to see if this unusual phenotype would be re-expressed after a temporary switching off. To switch off both expressed i-antigens, serotype transformation was induced in the F2 clones by shifting the culture temperature from 25 to 17 degrees C. Two weeks later, when the clones returned to the initial temperature conditions, each of them was seen to re-express both parental i-antigens. This result is discussed with reference to the role of i-antigens in regulation of their own expression as has been suggested by some authors. 相似文献