全文获取类型
收费全文 | 394807篇 |
免费 | 45463篇 |
国内免费 | 360篇 |
专业分类
440630篇 |
出版年
2016年 | 3573篇 |
2015年 | 5354篇 |
2014年 | 6246篇 |
2013年 | 8965篇 |
2012年 | 9950篇 |
2011年 | 10021篇 |
2010年 | 6669篇 |
2009年 | 6297篇 |
2008年 | 8912篇 |
2007年 | 9397篇 |
2006年 | 8933篇 |
2005年 | 8702篇 |
2004年 | 8623篇 |
2003年 | 8218篇 |
2002年 | 8218篇 |
2001年 | 18207篇 |
2000年 | 18760篇 |
1999年 | 14899篇 |
1998年 | 4910篇 |
1997年 | 5162篇 |
1996年 | 4815篇 |
1995年 | 4617篇 |
1994年 | 4553篇 |
1993年 | 4554篇 |
1992年 | 12062篇 |
1991年 | 11652篇 |
1990年 | 11309篇 |
1989年 | 10959篇 |
1988年 | 10344篇 |
1987年 | 9870篇 |
1986年 | 9375篇 |
1985年 | 9461篇 |
1984年 | 7814篇 |
1983年 | 6724篇 |
1982年 | 5353篇 |
1981年 | 4986篇 |
1980年 | 4522篇 |
1979年 | 7629篇 |
1978年 | 6156篇 |
1977年 | 5657篇 |
1976年 | 5342篇 |
1975年 | 6003篇 |
1974年 | 6636篇 |
1973年 | 6570篇 |
1972年 | 6093篇 |
1971年 | 5511篇 |
1970年 | 4759篇 |
1969年 | 4721篇 |
1968年 | 4305篇 |
1967年 | 3620篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
811.
812.
We have earlier demonstrated that a mixed population of immunologically specific killer cells, including cytotoxic T lymphocytes, non-T (“B”) lymphocytes and monocytes, infiltrate “sponge matrix” allografts at the peak of rejection on Day 8 after transplantation. We have now performed a sequential study covering both early and late stages of the rejection response. We demonstrate that the early infiltrating killer cells are sensitive to anti-Ø and anti-T cell serum plus complement treatment but the late killer cells are not. This finding indicates that the first cytotoxic host cells infiltrating the allograft are predominantly T lymphocytes, whereas as the rejection process proceeds also cytotoxic non-T (“B”) lymphocytes and monocytes are recruited to the site of inflammation. 相似文献
813.
Immune complex effects on murine macrophages. I. Immune complexes suppress interferon-gamma induction of Ia expression 总被引:8,自引:0,他引:8
H W Virgin G F Wittenberg E R Unanue 《Journal of immunology (Baltimore, Md. : 1950)》1985,135(6):3735-3743
We have studied the effects of immune complexes on the expression of macrophage surface proteins in vitro. Increased expression of the H-2 molecules I-A, I-E, and K on the macrophage membrane was induced by in vitro culture with crude lymphokine or interferon-gamma. Expression of all three of the molecules was additionally increased by stimulating the cultures with heat-killed Listeria monocytogenes. Addition of soluble immune complexes to the cultures did not have any effect on macrophage expression of these proteins. However, significant inhibition of lymphokine or interferon-gamma induction of I-A, I-E, and H-2K was observed when macrophages were cultured on plates to which immune complexes had been bound. This inhibition was dose dependent, required an immunoglobulin (Ig) molecule with an intact Fc portion, did not require the presence of T cells, and occurred in the presence of indomethacin. Complexes containing IgG1, IgG2a, IgG2b, and IgE, but not IgM or IgA, antibodies mediated the inhibitory effect. 相似文献
814.
Fast atom bombardment mass spectrometry (FAB-MS) has been used to measure positional isotope exchange rates in enzyme-catalyzed reactions. The technique has been applied to the reactions catalyzed by acetyl-CoA synthetase and argininosuccinate synthetase. The FAB technique is also able to quantitatively determine the oxygen-18 or oxygen-17 content of nucleotides on as little as 10 nmol of material with no prior derivatization. Acetyl-CoA synthetase has been shown by FAB-MS to catalyze the positional exchange of an oxygen-18 of ATP from the beta-nonbridge position to the alpha beta-bridge position in the presence of acetate. These results are consistent with acetyl adenylate as a reactive intermediate in this reaction. Argininosuccinate synthetase was shown not to catalyze a positional isotope exchange reaction designed to test for the formation of citrulline adenylate as a reactive intermediate. Argininosuccinate synthetase was also found not to catalyze the transfer of oxygen-18 from [ureido-18O]citrulline to the alpha-phosphorus of ATP in the absence of added aspartate. This experiment was designed to test for the transient formation of carbodiimide as a reactive intermediate. These results suggest that either argininosuccinate synthetase does not catalyze the formation of citrulline adenylate or the enzyme is able to completely suppress the rotation of the phosphoryl groups of PPi. 相似文献
815.
816.
817.
818.
Karlheinz Grillitsch Pablo Tarazona Lisa Klug Tamara Wriessnegger Günther Zellnig Erich Leitner Ivo Feussner Günther Daum 《生物化学与生物物理学报:生物膜》2014
Despite similarities of cellular membranes in all eukaryotes, every compartment displays characteristic and often unique features which are important for the functions of the specific organelles. In the present study, we biochemically characterized the plasma membrane of the methylotrophic yeast Pichia pastoris with emphasis on the lipids which form the matrix of this compartment. Prerequisite for this effort was the design of a standardized and reliable isolation protocol of the plasma membrane at high purity. Analysis of isolated plasma membrane samples from P. pastoris revealed an increase of phosphatidylserine and a decrease of phosphatidylcholine compared to bulk membranes. The amount of saturated fatty acids in the plasma membrane was higher than in total cell extracts. Ergosterol, the final product of the yeast sterol biosynthetic pathway, was found to be enriched in plasma membrane fractions, although markedly lower than in Saccharomyces cerevisiae. A further characteristic feature of the plasma membrane from P. pastoris was the enrichment of inositol phosphorylceramides over neutral sphingolipids, which accumulated in internal membranes. The detailed analysis of the P. pastoris plasma membrane is discussed in the light of cell biological features of this microorganism especially as a microbial cell factory for heterologous protein production. 相似文献
819.
Comparison of uptake kinetics in freshly isolated suspensions and short-term primary cultures of rat hepatocytes 总被引:2,自引:0,他引:2
The apparent kinetics of uptake of various model substrates were examined for hepatocytes in suspension and primary culture up to 72 h. The ability of hepatocytes to take up taurocholate and ouabain was decreased in culture. Vmax for uptake of both substrates diminished rapidly with increasing time in culture. An increase in Km was observed in cultures 6 h after plating, but there was no further change with prolongation of culture time. The decrease of uptake of taurocholate and ouabain during culture may be due to the reduction in the number of transport carriers plus a decrease of affinity of the carrier to substrates. The nonsaturable component of cadmium uptake was much reduced in cultured cells compared with the suspensions. The saturable process was lower in 6 h culture but increased to a level comparable with the fresh cells at longer culture time. No significant change was found in the Km between suspensions and cultures. Uptake of alpha-aminoisobutyric acid was greater in culture while that of 3-O-methyl-D-glucose was relatively stable but about one-half that found in cell suspension. Thus, uptake of two substrates, taurocholate and ouabain, is clearly compromised with increasing time in primary culture, while uptake of the other substrates does not reflect such a dramatic decrease. It is therefore apparent that the cell preparation of choice in uptake studies depends on the substrate and the nature of the experiments. 相似文献
820.