全文获取类型
收费全文 | 852071篇 |
免费 | 97654篇 |
国内免费 | 352篇 |
专业分类
950077篇 |
出版年
2016年 | 9182篇 |
2015年 | 12642篇 |
2014年 | 15050篇 |
2013年 | 21856篇 |
2012年 | 23962篇 |
2011年 | 24460篇 |
2010年 | 16434篇 |
2009年 | 15360篇 |
2008年 | 21853篇 |
2007年 | 23087篇 |
2006年 | 21594篇 |
2005年 | 20812篇 |
2004年 | 20804篇 |
2003年 | 20201篇 |
2002年 | 19700篇 |
2001年 | 34935篇 |
2000年 | 35458篇 |
1999年 | 28446篇 |
1998年 | 10406篇 |
1997年 | 10937篇 |
1996年 | 10494篇 |
1995年 | 10031篇 |
1994年 | 9942篇 |
1993年 | 9862篇 |
1992年 | 24978篇 |
1991年 | 24746篇 |
1990年 | 24533篇 |
1989年 | 24004篇 |
1988年 | 22422篇 |
1987年 | 21478篇 |
1986年 | 20125篇 |
1985年 | 20645篇 |
1984年 | 17218篇 |
1983年 | 15052篇 |
1982年 | 11678篇 |
1981年 | 10778篇 |
1980年 | 10083篇 |
1979年 | 16929篇 |
1978年 | 13289篇 |
1977年 | 12399篇 |
1976年 | 11790篇 |
1975年 | 12961篇 |
1974年 | 13796篇 |
1973年 | 13548篇 |
1972年 | 12767篇 |
1971年 | 11283篇 |
1970年 | 9865篇 |
1969年 | 9513篇 |
1968年 | 8822篇 |
1967年 | 7676篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Iu G Kaz'mina S A Salamatova M M Liubinskaia E V Chernokhvostova 《Zhurnal mikrobiologii, epidemiologii, i immunobiologii》1984,(8):83-88
The possibility of inducing systemic tolerance in animals by feeding them with ovalbumin and human serum was studied on mice, rats and rabbits. Antibodies to ovalbumin, human serum albumin and immunoglobulins (IgG, IgA, IgM) were determined by the passive hemagglutination test in the sera of the test and control animals after the second immunization made through a parenteral route. Tolerance to all the antigens under study was obtained in mice and rats, while in rabbits such feeding was found to produce the priming effect. The degree of tolerance was the greater, the more was the dose of the antigen and the longer was the period of feeding. Different proteins showed varying tolerogenic activity; the same degree of tolerance in mice was obtained by feeding them with IgG in a dose of 0.3-0.5 mg and with ovalbumin or human serum albumin in a dose of 6-12 mg (per gram of body weight). Tolerance was determined on day 3 after the course of feeding was over; in 3 weeks tolerance essentially decreased, and in 1.5-2 months it was replaced by normal reactiveness. Tolerance induced by the oral administration of antigens proved to be immunologically specific. 相似文献
993.
The population dynamics of Heterodera glycines as influenced by alachlor, fenamiphos, and ethoprop alone and in herbicide-nematicide combinations were studied in the field. Numbers of H. glycines juveniles and eggs were higher at midseason and harvest where nematicides were applied. Fenamiphos alone or in combination with alachlor provided better control of H. glycines and greater seed yields than treatments with ethoprop. Numbers of H. glycines eggs at harvest in 1980 were positively correlated with numbers of juveniles at planting in 1981 and negatively related to seed yield in 1981. 相似文献
994.
995.
R Page L W Frazier T Yorio 《Comparative biochemistry and physiology. A, Comparative physiology》1988,91(1):53-59
1. The northern leopard frog, Rana pipiens, pipiens, in contrast to the southern leopard frog, Rana pipiens, berlandieri, did not demonstrate any significant H+ excretion across its integument even during a challenge of chronic metabolic acidosis. Likewise, no increase in the number of H+ secreting mitochondria-rich cells were observed in the northern frogs. 2. Under normal acid-base conditions in the southern frogs, H+ excretion was found to be dependent on mucosal sodium concentrations, whereas during chronic metabolic acidosis, H+ excretion was independent of mucosal sodium concentrations, but was amiloride sensitive. 3. High salinity adapted southern frogs, under normal and acidotic conditions, had enhanced H+ excretion rates as compared to the control non-salt adapted frogs. 4. Blood analyses demonstrated that significant acid-base changes were the result of systemic acidosis and not due to salt adaptations. Blood Na+ and K+ concentrations were also efficiently maintained during salt adaptations or chronic metabolic acidosis. 5. The results suggest that H+ excretion in epithelia can be influenced by the sodium transport state of the cell and the systemic acid-base profile. Models are proposed explaining these relationships. 相似文献
996.
A simple and accurate technique for the determination of the heat resistance of spores is described. The technique combines a modified capillary tube method with a solid heating block. The come-up time of spore suspensions was found to be short and simple and accurate technique is suggested for the correction of the come-up times. Experimental results are presented for the destruction of spores of Bacillus stearothermophilus at 120 which indicates the accuracy and reproducibility of the new method. 相似文献
997.
The finger and palmar prints of 60 women with breast carcinoma were studied. The results were compared with two groups of
healthy women, the first consisted of old women and the second of young women. The dermatoglyphics seem to be of little use
in the diagnosis of cancers of ectodermic origin.
Supported by M.P.I. 60%, 1983 相似文献
998.
Background
In heterogeneous environments, sex-biased dispersal could lead to environmental adaptive parental effects, with offspring selected to perform in the same way as the parent dispersing least, because this parent is more likely to be locally adapted. We investigate this hypothesis by simulating varying levels of sex-biased dispersal in a patchy environment. The relative advantage of a strategy involving pure maternal (or paternal) inheritance is then compared with a strategy involving classical biparental inheritance in plants and in animals. 相似文献999.
Inheritance of barley nuclear genes responsible for various morphological marker traits was studied in hybrid populations F2 and Fa. Nine marker genes showed deviation from Mendelian monogenic inheritance depending on the cross direction and maternal cytoplasm. Segregation biases to both recessive mutant and dominant normal phenotypes were observed. Mechanisms of the segregation bias related to cytoplasm substitution in iso- and alloplasmic lines are discussed. 相似文献
1000.
Factor 390 chromophores: phosphodiester between AMP or GMP and methanogen factor 420 总被引:9,自引:0,他引:9
Two chromophores with absorbance maxima at 390 nm (factors 390) have been isolated from oxidized cells of Methanobacterium thermoautotrophicum delta H. The isolation procedure included anion-exchange chromatography of the soluble cofactor pool followed by reverse-phase chromatography. The factor 390 species are novel derivatives of methanogen coenzyme factor 420 in which the 5-deazaflavin 8-hydroxy group is in a phosphodiester linkage to adenosine 5'-phosphate or guanosine 5'-phosphate. The structural assignments were based, in part, on the UV-visible and 1H NMR spectra. In addition, the results from amino acid analysis, phosphate determination, 31P NMR spectroscopy, and fast atom bombardment mass spectrometry were consistent with the proposed structures. Confirmation of the factor 390 structures was made following phosphodiesterase release of the nucleotide monophosphates from factor 420. The nucleotide monophosphates were identified as AMP and GMP by UV-visible spectra and based on elution position by using reverse-phase and anion-exchange high-performance liquid chromatography. The presence of AMP was further demonstrated by using adenylate-5'-phosphate kinase which induced a spectral shift during conversion of the sample to IMP. In addition, the presence of GMP was established by a specific enzymatic assay. 相似文献