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   29445篇
  免费   3744篇
  国内免费   30篇
  2016年   257篇
  2015年   333篇
  2014年   416篇
  2013年   686篇
  2012年   662篇
  2011年   725篇
  2010年   501篇
  2009年   423篇
  2008年   613篇
  2007年   668篇
  2006年   633篇
  2005年   631篇
  2004年   636篇
  2003年   656篇
  2002年   660篇
  2001年   1871篇
  2000年   1843篇
  1999年   1449篇
  1998年   479篇
  1997年   479篇
  1996年   483篇
  1995年   427篇
  1994年   427篇
  1993年   423篇
  1992年   1072篇
  1991年   1090篇
  1990年   1069篇
  1989年   1035篇
  1988年   967篇
  1987年   904篇
  1986年   776篇
  1985年   750篇
  1984年   588篇
  1983年   511篇
  1982年   371篇
  1981年   346篇
  1980年   332篇
  1979年   572篇
  1978年   455篇
  1977年   413篇
  1976年   340篇
  1975年   457篇
  1974年   472篇
  1973年   425篇
  1972年   396篇
  1971年   313篇
  1970年   258篇
  1969年   242篇
  1968年   227篇
  1967年   205篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
The monoclonal antibody FDO161G reacts with a 43-kDa protein found in human extravillous trophoblast, syncytiotrophoblast, adrenal cortex, interstitial cells of the testis and ovarian follicle cumulus cells. cDNAs for this protein have been isolated from the lambda gt11 library, sequenced, and expressed in COS-7 cells. The protein was identified as 3 beta-hydroxy-5-ene steroid dehydrogenase (HSD). The sequence of the HSD protein raises questions about its association with cell membrane systems. The lack of reactivity of FDO161G with other tissues suggests that HSD has a limited tissue distribution and that other enzymes may exist in peripheral tissues, which can convert delta 5 3-hydroxysteroids to delta 4 3-ketosteroids.  相似文献   
72.
Plasma Na, K, Cl, Ca, P didn't or moderately be altered by exposure to acute heat in sauna bath (20 mn, 80 degrees C, relative humidity 15-20%). However, CO2T decreased, ARP, aldosterone, ACTH, PRL increased, and PTH wasn't modified.  相似文献   
73.
In this study it is shown that the higher molecular weight previously reported for tiger shark carbonic anhydrase (carbonate hydro-lyase, EC 4.2.1.1) compared to other carbonic anhydrases is decreased to a normal value around 30 000 after disulfide reduction of the enzyme. This difference in molecular weight is at least partly due to the existence of disulfide-linked glutathione and cysteine residues. Approx. 3 mol glutathione and a similar amount of cysteine are shown to be bound per mol enzyme. The presence of these factors also has effects on the enzyme activity.  相似文献   
74.
75.
76.
Platinum(II) binding to metallothioneins   总被引:1,自引:0,他引:1  
The reaction of equine renal metallothionein (MT) with excess K2PtCl4 at pH 2 results in a polymeric adduct containing 17 +/- 2 mol Pt/mol MT. A monomeric adduct containing 7 mol Pt/mol MT is obtained at neutral pH. Rates of reaction of Pt7MT with DTNB and iodoacetic acid are consistent with Pt2+ to cysteine thiolate coordination, and the extent of reaction in both cases is 11 +/- 2 mol cys/mol MT. Adducts from the reaction of K2PtCl4 with apoMT chemically modified at the N-terminal methionine residue, Cd7MT, and native MT are also reported. A structural model of Pt7MT is proposed in which the square planar tetrathiolate Pt(II) unit is incorporated into a three-metal beta cluster. Implications for the metabolism of platinum anticancer drugs are discussed.  相似文献   
77.
The influence of orotic acid on post-excitatory facilitation of evoked potentials released by electric stimulation of the tooth pulp in the sensomotor cortex was studied. 15-360 min following application of 100 mg/kg orotic acid, increase in amplitude of potentials released by stimulation of the tooth pulp, reinforcement of the post-excitatory facilitation observable 5 msec after stimulation occurred.  相似文献   
78.
The properties of the pH 4.0 endonuclease from adenovirus-type-2-infected KB cells were determined. The enzyme has a molecular weight of approximately 40000. Its pH optimum is at pH 4.0, it is not inhibited by ethylenediaminetetraacetate (EDTA), and it is active at temperatures up to 60 degree C. The enzyme cleaves adenovirus DNA in a stepwise manner. The limit digestion product has a molecular weight of 120000-200000. There is evidence that the cleavage reaction proceeds via an initial single-strand nick. Under the conditions tested the endonuclease did not seem to reveal a high degree of specificity as to the recognition of cleavage sites, or else the sites recognized occurred very frequently.  相似文献   
79.
80.
The interaction of human red blood cells (RBCs) with diethylenetriamine-pentaacetic acid (DTPA) or its Gd-complex (Magnevist, a widely used clinical magnetic resonance contrast agent containing free DTPA ligands) led to the following, obviously interrelated phenomena. (i) Both compounds protected erythrocytes against electrohemolysis in isotonic solutions caused by a high-intensity DC electric field pulse. (ii) The inhibition of electrohemolysis was observed only when cells were electropulsed in low-conductivity solutions. (iii) The uptake of Gd-DTPA by electropulsed RBCs was relatively low. (iv) (Gd-) DTPA reduced markedly deformability of erythrocytes, as revealed by the electrodeformation experiments using high-frequency electric fields. Taken together, the results indicate that (Gd-) DTPA produce stiffer erythrocytes that are more resistant to electric field exposure. The observed effects of the chelating agents on the mechanical properties and the electropermeabilization of RBCs must have an origin in molecular changes of the bilayer or membrane-coupled cytoskeleton, which, in turn, appear to result from an alteration of the ionic equilibrium (e.g., Ca2+ sequestration) in the vicinity of the cell membrane. Received: 19 January 1999/Revised: 1 April 1999  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