首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1390584篇
  免费   124342篇
  国内免费   1941篇
  1516867篇
  2021年   17953篇
  2019年   16208篇
  2018年   17993篇
  2017年   16714篇
  2016年   28277篇
  2015年   42735篇
  2014年   50805篇
  2013年   77096篇
  2012年   39306篇
  2011年   28576篇
  2010年   44440篇
  2009年   45560篇
  2008年   26759篇
  2007年   24811篇
  2006年   29736篇
  2005年   30693篇
  2004年   29936篇
  2003年   27259篇
  2002年   25253篇
  2001年   34956篇
  2000年   32296篇
  1999年   32158篇
  1998年   25617篇
  1997年   25532篇
  1996年   24978篇
  1995年   23160篇
  1994年   22900篇
  1993年   22012篇
  1992年   28090篇
  1991年   26653篇
  1990年   25349篇
  1989年   25988篇
  1988年   23876篇
  1987年   22529篇
  1986年   21625篇
  1985年   23335篇
  1984年   22994篇
  1983年   20346篇
  1982年   20584篇
  1981年   19778篇
  1980年   18517篇
  1979年   18998篇
  1978年   18035篇
  1977年   17157篇
  1976年   16318篇
  1975年   16129篇
  1974年   16649篇
  1973年   16959篇
  1972年   14404篇
  1971年   13287篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
711.
The growth-associated protein B-50 also termed GAP-43, F1, pp46, P-57 and neuromodulin is a nervous tissuespecific protein kinase C (PKC) substrate that is considered to play a major role in neurite formation, regeneration, and neuroplasticity. We describe the isolation of seven mouse monoclonal antibodies (Mabs) directed against B-50. The Mabs are produced against the bovine B-50, selected by ELISA for cross-reactivity with its human counterpart, and evaluated on Western blots in comparison with the well-characterized affinity-purified rabbit polyclonal antibodies to rat-B-50. The Western blots show that the Mabs NM1, NM4, and NM6 recognize specifically the B-50 of bovine, human, and rat brain extract and the purified PKC phosphorylated and unphosphorylated rat B-50 isoforms. The Mabs NM2 and NM3 cross-react with bovine B-50 immunoreactive c-kinase substrate (BICKS), a protein sharing a 17 amino acid sequence homology with B-50. Two Mabs are useful for the detection of B-50 immunoreactivity in formalin-fixed human and rat brain tissues. In human specimen of the hippocampus, a characteristic neuropil distribution of B-50 is detected by the Mabs. In human muscle, Mabs reveal B-50 in nerve bundles and in axons at motor end plates. Thus, these Mabs are useful in investigating the function and localization of the B-50 protein.  相似文献   
712.
Abstract Glycoproteins are providing to be quite common in prokaryotes. Those is S-layers are the best understood in terms of structure. Numerous eubacteria produce non-S-layer glycoproteins about which relatively little is known. The glycans on such protein and the nature and sites of their linkages to protein are novel in those glycoproteins which have been examined in any detail. The possible functions of the glycans are mostly not understood. Eubacterial non-S-layer glycoproteins and the glycosylation systems producing them observe more attention.  相似文献   
713.
In a patient with the Zollinger-Ellison syndrome who had undergone vagotomy, pyloroplasty and, later, gastrojejunostomy, epigastric pain and stomal ulceration recurred despite the use of high doses (2700 mg/d) of cimetidine. Ranitidine, a new histamine H2-receptor antagonist, reversed all symptoms and healed the stomal ulcer without side effects, thus obviating the need for further surgery. Ranitidine may prove to be the drug of choice in the medical management of patients with the Zollinger-Ellison syndrome.  相似文献   
714.
715.
J Molnar  M Z Lai  G E Siefring  L Lorand 《Biochemistry》1983,22(25):5704-5709
Plasma fibronectin is one of the largest plasma proteins (Mr approximately 440 000), comprising two approximately equal polypeptide chains which are held together by a disulfide linkage near the C-terminal end of the molecule. The binding of gelatinized latex beads to liver slices as well as the internalization of these particles by macrophages, in the presence of heparin, is greatly enhanced by fibronectin. The question as to whether the entire covalent structure of fibronectin was necessary for opsonizing activity was approached by limited proteolytic degradations of the molecule. Patterns of controlled digestion with trypsin, cathepsin D, Staphylococcus aureus protease, and plasmin all indicate that the minimal unit necessary for retention of opsonic activity is some large (Mr 200 000 and 190 000) single-chain entity. Treatment with plasmin proved to be the most reliable procedure for generating the active split product which could be readily separated from the inactive, disulfide-containing C-terminal fragment. Incorporation of dansylcadaverine into plasma fibronectin (3.5 mol/mol of protein) by fibronoligase (coagulation factor XIIIa) did not affect the opsonic activity of the protein.  相似文献   
716.
717.
718.
The influence of age, weaning, season of the year and body weight on the peripheral levels of progesterone, oestradiol-17β and luteinizing hormone (LH) were studied during neonatal, perinatal and peripubertal periods in buffalo heifers. The buffalo heifers exhibited oestrus only after 30 months of age and had higher levels of LH and oestradiol-17β and a lower level of progesterone on the day of oestrus. The progesterone concentration was affected significantly (P < 0.01) by different seasons, by weaning (P < 0.05) and varied between pubertal and neonatal periods (P < 0.01), whereas the oestradiol-17β level was affected significantly (P < 0.01) by weaning and varied at different seasons and with body weight. However, the LH concentration was greater during the neonatal period than the pre- and peripubertal periods and changed significantly (P < 0.01) between groups of ages and body weights. The results suggest that increases in the levels of oestradiol-17β and progesterone after 30 months of age are probably indicative of the onset of puberty in buffalo heifers. However, a further increase in oestradiol-17β, LH, and a decrease in progesterone are essential for oestrus and cyclicity to be exhibited in buffalo heifers.  相似文献   
719.
720.
Volume and density changes of biological fluids with temperature   总被引:3,自引:0,他引:3  
High-precision (10(-5) g/ml) mass density measurements on human blood, plasma, plasma ultrafiltrate (using PM-10 membranes), and erythrocyte concentrate samples were performed with the mechanical oscillator technique. Measurement temperatures varied between 4 and 48 degrees C and were accurate to +/- 1 X 10(-2) K. The coefficient of thermal expansion (beta), defined as relative volume change with temperature, was calculated. It was shown that beta increases with temperature in these fluid samples over the entire temperature range investigated; the magnitude of this increase declines with increasing temperature; beta increases with density at temperatures below 40 degrees C but is independent of density above 40 degrees C; and the beta of the intracellular fluid has about twice the value of the beta for extracellular fluid at low (4-10 degrees C) temperatures but is equal for both fluids at greater than or equal to 40 degrees C. The mechanical oscillator technique provides data with an accuracy sufficient to perform precise (10(-5) K) calculations of beta of small volumes of biological fluids.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号