全文获取类型
收费全文 | 4755篇 |
免费 | 470篇 |
国内免费 | 1篇 |
出版年
2023年 | 19篇 |
2022年 | 30篇 |
2021年 | 71篇 |
2020年 | 69篇 |
2019年 | 73篇 |
2018年 | 83篇 |
2017年 | 59篇 |
2016年 | 127篇 |
2015年 | 185篇 |
2014年 | 205篇 |
2013年 | 253篇 |
2012年 | 332篇 |
2011年 | 322篇 |
2010年 | 180篇 |
2009年 | 191篇 |
2008年 | 256篇 |
2007年 | 236篇 |
2006年 | 237篇 |
2005年 | 229篇 |
2004年 | 243篇 |
2003年 | 216篇 |
2002年 | 227篇 |
2001年 | 63篇 |
2000年 | 60篇 |
1999年 | 79篇 |
1998年 | 73篇 |
1997年 | 49篇 |
1996年 | 55篇 |
1995年 | 62篇 |
1994年 | 44篇 |
1993年 | 54篇 |
1992年 | 43篇 |
1991年 | 44篇 |
1990年 | 57篇 |
1989年 | 42篇 |
1988年 | 41篇 |
1987年 | 36篇 |
1986年 | 29篇 |
1985年 | 44篇 |
1984年 | 40篇 |
1983年 | 43篇 |
1982年 | 31篇 |
1981年 | 36篇 |
1980年 | 18篇 |
1979年 | 21篇 |
1978年 | 20篇 |
1977年 | 27篇 |
1976年 | 23篇 |
1974年 | 21篇 |
1973年 | 17篇 |
排序方式: 共有5226条查询结果,搜索用时 15 毫秒
41.
Apparatus for the partial freezing of liquid nitrogen for the rapid cooling of cells and tissues 总被引:2,自引:0,他引:2
A P MacKenzie 《Biodynamica》1969,10(215):341-351
42.
43.
44.
Litigation for personal injury following accidental trauma is an expensive and confused process involving three protagonists: patient, doctor and lawyer. Although post-traumatic conditions can be elaborately classified, the intrinsic validity of such classifications is often questionable. Current methods of evaluating psychological sequelae of accidental injury are inaccurate and unsatisfactory, partly because of the protagonists'' conceptual, motivational and semantic differences. In addition, there is no really satisfactory method of (a) determining and quantifying minor but significant degrees of brain damage, (b) distinguishing these from “post-traumatic neurosis”, or (c) determining the relationship between the trauma and subsequent disturbance of function. Increasingly “expert” advice is solicited but owing to the nature of the data and conditions of examination, such advice does little to clarify the underlying problems. Furthermore, doctors are often unable to communicate effectively to the judiciary just how the trauma has affected the patient. Even though certain suggestions for improvement are advanced, the need for comprehensive, longitudinal research is inescapable. 相似文献
45.
46.
Marion Barclay R. K. Barclay V. P. Skipski Olga Terebus-Kekish C. H. Mueller Ellen Shah W. L. Elkins 《The Biochemical journal》1965,96(1):205-209
1. Lipoproteins were measured in sera from 11 young women having a similar environment and diet. Sera were obtained at weekly intervals over a 12-week period. The values of the lipoproteins during periods in the normal ovulatory cycle were compared to assess their relation to reported hormone concentrations in blood. 2. Only the 4–0sf (HDL2) (d 1·125 sodium chloride) fraction changed significantly; it increased at ovulation in ten of the 11 subjects and fell as menstruation approached. 3. There was greater variability in most of the low-density rather than the high-density lipoproteins within individuals. The lipoprotein class most characteristic for an individual was the 4–0sf or HDL2 fraction. 相似文献
47.
Jean-Louis Connat Ellen Marie Dotson Peter Allan Diehl 《Archives of insect biochemistry and physiology》1989,10(3):I-XV
Fifth (last) instar nymphs of th e tick Ornithodoros moubata convert ingested 20-hydroxyecdysone (20E) to apolar conjugates AP2, which are then converted to th e more polar conjugates API. Only small quantities of free hormone were transferred to th e hemolymph and the carcass within t h e first 2 days after the blood meal. The proportion of radiolabel in these two compartments was highest at the time of the endogenous ecdysteroid peak; however, no traces of free [3H]20E were detected. The conversion probably occurs principally in the intestinal cells. Eleven days after ingestion, 84% of the radiolabel is located in the digestive tract, mainly in the form of API conjugates. API obtained in second instar nymphs fed with [3H]ecdysone ([3H]E) remain stable throughout the following nymphal instars. The ecdysteroid moiety of APT remained unchanged. The hydrolysis, although not complete, always yielded a peak comigrating with the reference E but never 20E or any other clearly distinct peaks that may have corresponded to metabolites of 20E. Less label per individual was present in adults, but its nature remained the same, viz., API mainly located in the digestive tract. In females, 2.5% of the label was transferred to the progeny during the first ovipositional cycle. Apolar products (mainly AP2) that accumulated in eggs of females injected with [3H]E or [3H]20E during vitellogenesis remained unchanged during the whole embryonic development. During the molting cycle of larvae, there was only a slight conversion of AP2 to API, but esterase hydrolysis of these products released the same percentages of E and 20E as in the freshly laid eggs. We conclude that in this tick species apolar conjugates of ecdysteroids are inactivation metabolites that are not reutilized during the development of the animal. These metabolites are mainly retained in the tick, probably because of its peculiar blocked midgut. Several studies have shown that in other arthropod species (ticks, spiders, and insects), these apolar metabolites are excreted in the feces. 相似文献
48.
Jacqueline Jollès Ellen M. Prager Emad S. Alnemri Pierre Jollès Ibrahim M. Ibrahimi Allan C. Wilson 《Journal of molecular evolution》1990,30(4):370-382
Summary Complete amino acid sequences are presented for lysozymesc from camel and goat stomachs and compared to sequences of other lysozymesc. Tree analysis suggests that the rate of amino acid replacement went up as soon as lysozyme was recruited for the stomach function in early ruminants. The two lysozymes from goat stomach are the products of a gene duplication that probably took place before the divergence of cow, goat, and deer about 25 million years ago. Partial sequences of three lysozymes from goat tears indicated that (a) the goat tear family of lysozymes may have diverged from the stomach lysozyme family by an ancient duplication and (b) later duplications are probably responsible for the multiple forms of tear and milk lysozymes in ruminants. 相似文献
49.
The role of indole-3-butyric acid (IBA) in adventitious root formation was studied by analyzing the uptake and subsequent metabolism of IBA in shoots of M.26 apple (Malus pumila Mill.) rootstock grown in vitro. Roots were induced by exposing shoots to 4 M IBA and [3H]IBA for 5 days in the dark and then transferring them to plant growth regulator (PGR)-free medium in the light until roots formed. Approximately 50% of the total radioactivity applied was taken up from the agar medium by the shoots during the 5-day incubation period in IBA. Indole-3-butyric acid metabolism was studied by extraction and high-performance liquid chromatographic (HPLC) separation of [3H]IBA and metabolites from the basal sections of treated shoots. The major [3H]IBA metabolite co-eluted with authentic [14C]indole-3-acetic acid (IAA) suggesting that IBA was converted to IAA in the shoots. The proportion of newly synthesized IAA present as conjugates was higher at the end of the 5-day IBA treatment period than after 13 days in PGR-free medium. There appeared to be no conjugation of IBA at any time. 相似文献
50.
R Szabo E Todd J MacKenzie L Parrington A Armstrong 《Applied and environmental microbiology》1990,56(11):3546-3549
Several strains of Escherichia coli O157:H7 artificially inoculated into vegetables and dairy products were recovered on hydrophobic grid membrane filters and enumerated by an enzyme-labeled antibody assay. The mean of the recoveries from 12 fresh vegetables was 108.8%, whereas that from 10 dairy products was 93.2%. Modified tryptic soy broth at 43 degrees C with shaking at 100 rpm provided optimum recovery of the organism from meat, with a sensitivity of less than or equal to 1 CFU/g, which is 10 times more sensitive than direct plating. The method performed equally well with vegetable and dairy products. Tryptic soy broth, however, under the same conditions gave the best results for fecal samples. Of 22 asymptomatic dairy cattle, reported as having positive Brucella titers when assayed with polyclonal antibodies, eight were found to contain E. coli O157 in their feces as demonstrated by the enzyme-labeled antibody assay by using monoclonal antibodies. This finding may explain some of the false-positive Brucella tests. 相似文献