全文获取类型
收费全文 | 18467篇 |
免费 | 920篇 |
国内免费 | 27篇 |
专业分类
19414篇 |
出版年
2024年 | 31篇 |
2023年 | 164篇 |
2022年 | 375篇 |
2021年 | 703篇 |
2020年 | 414篇 |
2019年 | 441篇 |
2018年 | 643篇 |
2017年 | 602篇 |
2016年 | 784篇 |
2015年 | 886篇 |
2014年 | 1128篇 |
2013年 | 1547篇 |
2012年 | 1630篇 |
2011年 | 1434篇 |
2010年 | 830篇 |
2009年 | 728篇 |
2008年 | 840篇 |
2007年 | 813篇 |
2006年 | 681篇 |
2005年 | 617篇 |
2004年 | 499篇 |
2003年 | 414篇 |
2002年 | 372篇 |
2001年 | 307篇 |
2000年 | 279篇 |
1999年 | 254篇 |
1998年 | 100篇 |
1997年 | 76篇 |
1996年 | 82篇 |
1995年 | 77篇 |
1994年 | 57篇 |
1993年 | 56篇 |
1992年 | 152篇 |
1991年 | 143篇 |
1990年 | 113篇 |
1989年 | 85篇 |
1988年 | 126篇 |
1987年 | 97篇 |
1986年 | 80篇 |
1985年 | 81篇 |
1984年 | 81篇 |
1983年 | 46篇 |
1982年 | 40篇 |
1981年 | 47篇 |
1980年 | 43篇 |
1979年 | 56篇 |
1978年 | 35篇 |
1977年 | 43篇 |
1976年 | 31篇 |
1974年 | 29篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
161.
Active transport of calcium ions has been demonstrated in inside-out membrane vesicles from Mycobacterium phlei mediated by respiratory linked substrates as well as by ATP hydrolysis. The uptake of calcium exhibited an apparent Km of 80 microM and V of 16.6 nmol calcium uptake x min-1 x mg protein-1. A fortyfold concentration gradient for calcium ions was calculated for both the ATP-induced and the respiration-induced transport of calcium. Removal of coupling-factor-latent ATPase resulted in the complete loss of ATP-driven Ca2+ transport whereas the respiration-driven uptake was reduced by 40-50%. The uptake of calcium was inhibited by the proton conducting ionophores carbonylcyanide m-chlorophenylhydrazone and Gramicidin-D. The accumulated calcium was freely exchangeable with external calcium and was rapidly released by the addition of inhibitors of energy transduction, proton-translocating uncouplers or the ionophore A23187. The uptake of the weak base, methylamine, upon the oxidation of respiratory-linked substrates or the hydrolysis of ATP showed the generation of a protein gradient (inside acidic) which was partially collapsed on the addition of calcium ions. These results suggest that a Ca2+/H+ antiport mechanism may be responsible for the transport of calcium. 相似文献
162.
163.
164.
The present study was carried out to determine the detailed histological and cytological features of the excurrent ducts of
the male reproductive system in the rhesus monkey. The excurrent ducts show a regional difference in their histological features.
The use of some of these features as histological markers and their possible functional significance are discussed.
The epithelial cells in the different components of the excurrent duct system possess cytological features which suggest their
involvement in absorption and the secretion of different products into the lumen. 相似文献
165.
166.
167.
As a prerequisite to examining mRNA metabolism in compensatory renal hypertrophy, polyadenylated RNA has been purified from normal mouse kidney polysomal RNA by selection on oligo(dT)-cellulose. Poly(A)-containing RNA dissociated from polysomes by treatment with 10 mM EDTA and sedimented heterogeneously in dodecyl sulfate-containing sucrose density gradients with a mean sedimentation coefficient of 20 S. Poly(A) derived from this RNA migrated at the rate of 6-7 S RNA in dodecyl sulfate-containing 10% polyacrylamide gels. Coelectrophoresis of poly(A) labeled for 90 min with poly(A) labeled for 24 h indicated the long-term labeled poly(A) migrated faster than pulse-labeled material. Twenty percent of the cytoplasmic poly(A)-containing mRNA was not associated with the polysomes, but sedimented in the 40-80 S region (post-polysomal). Messenger RNA from the post-polysomal region had sedimentation properties similar to those of mRNA prepared from polysomes indicating post-polysomal mRNA was not degraded polysomal mRNA. Preliminary labeling experiments indicated a rapid equilibration of radioactivity between the polysomal and post-polysomal mRNA populations, suggesting the post-polysomal mRNA may consist of mRNA in transit to the polysomes. 相似文献
168.
169.
S Kumar 《Biochemical and biophysical research communications》1975,66(3):1063-1068
Substitution of tryptophan9 in ACTH1–24 by isoleucine results in complete loss of biological activity. A dose of 3.4 × 10?5 M per ml fails to stimulate corticosterone and cyclic AMP production. This analogue inhibits cyclic AMP production and corticosterone production induced by ACTH1–24 in isolated adrenal cortex cells. The I50 values for corticosterone and cyclic AMP inhibition are 2.3 × 10?6 M and 3.4 × 10?6 M respectively. 相似文献
170.
As an initial step towards understanding the role of mRNP complexes in translational regulation during compensatory renal hypertrophy, characteristics of polysome-associated mRNP isolated by affinity chromatography were studied. Renal mRNP contained 15–30% of the counts after a 1 hr pulse with 3H-orotic acid; it sedimented mainly between 10S and 100S and had a buoyant density of 1.42–1.44 g/cm3. RNA derived from the mRNP sedimented between 5S and 40S on sucrose density gradients, with the greatest radioactivity in the region of 15S. After labeling with 3H-adenine for 1 hr, up to 17% of the radioactivity present in the mRNP-associated RNA was resistant to digestion by pancreatic and T1 ribonucleases. The mRNP protein moiety contained six polypeptides with molecular weights 69,000, 75,000, 80,000, 100,000, 109,000, and 118,000 daltons, which were undetected in the material not binding to oligo(dT)-cellulose. 相似文献