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   425766篇
  免费   47902篇
  国内免费   164篇
  473832篇
  2018年   3928篇
  2016年   5307篇
  2015年   6929篇
  2014年   8182篇
  2013年   11286篇
  2012年   12829篇
  2011年   13276篇
  2010年   9113篇
  2009年   8464篇
  2008年   12169篇
  2007年   12670篇
  2006年   11873篇
  2005年   11356篇
  2004年   11395篇
  2003年   10671篇
  2002年   10495篇
  2001年   17452篇
  2000年   17465篇
  1999年   13936篇
  1998年   5028篇
  1997年   5287篇
  1996年   4921篇
  1995年   4625篇
  1994年   4491篇
  1993年   4544篇
  1992年   11628篇
  1991年   11547篇
  1990年   11314篇
  1989年   10924篇
  1988年   10494篇
  1987年   10089篇
  1986年   9379篇
  1985年   9236篇
  1984年   7757篇
  1983年   6710篇
  1982年   5163篇
  1981年   4617篇
  1980年   4467篇
  1979年   7425篇
  1978年   5864篇
  1977年   5401篇
  1976年   5203篇
  1975年   5596篇
  1974年   6307篇
  1973年   6172篇
  1972年   5767篇
  1971年   5226篇
  1970年   4634篇
  1969年   4578篇
  1968年   4422篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
911.
A previous experiment (Herzfeld & Taub, 1977) demonstrated that slide projections and explicit suggestions relating to thermal experiences can significantly augment temperature self-regulations training (.5 degrees F, p less than .05). however, the experimental design was thought to result in an underestimate of the magnitude of the effect, since each subject served as his own control and could therefore make use on nonsuggestion training days of material provided on training days. In this experiment, separate groups of subjects either were given feedback combined with the suggestion procedure on each of 8 training days or were given feedback alone. The mean temperature self-regulation of the suggestion group (2.01 degrees F) was significantly better than the self-regulation (.73) of the nonsuggestion group (t test, p less than 0.01), a difference of 1.28 degrees F.  相似文献   
912.
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   
913.
Recent data have demonstrated that differences in sIg density on B lymphocytes distinguish functionally distinct subpopulations of these cells. Other reports suggest that cyropreservation may change the frequency of sIg-bearing lymphocytes. To determine if cryopreservation alters either the frequency of sIg cells or the distribution of sIg density, PBM from normals and patients with CLL and LCL were analyzed using the FACS. Aliquots of Ficoll-Hypaque-separated PBM were controlled-rate frozen (1 °C/min) in 7.5% Me2SO in RPMI 1640 and thawed in a 37 °C water bath on the same day. Fresh and frozen-thawed PBM aliquots were labeled with fluorescein conjugates of F(ab′) fragments of affinity chromatography-purified anti-Fab or class-specific anti-μ, anti-δ, anti-γ, or anti-α. Histograms of relative cell fluorescence, reflecting sIg density, were prepared for each aliquot with the FACS. The frequency of sIg-bearing PBM labeled with each reagent was not significantly altered by freezing. Likewise, FACS profiles demonstrated that the distribution of sIg density on normal and CLL PBM was unchanged after freezing. However, the fluorescence peak produced by frozen-thawed unlabeled cells was occasionally slightly broader than that of fresh cells, suggesting increased autofluorescence induced by freezing. These data indicate that frozen cell preparations may be utilized for the study of B-lymphocyte subsets as determined by sIg density.  相似文献   
914.
915.
Recent theoretical work on the cooperative equilibrium binding of myosin subfragment-1-ADP to regulated actin, as influenced by Ca2+, is extended here to the cooperative steady-state ATPase activity of myosin subfragment-1 on regulated actin. Exact solution of the general steady-state problem will require Monte Carlo calculations. Three interrelated special cases are discussed in some detail and sample computer (not Monte Carlo) solutions are given. The eventual objective is to apply these considerations to in vitro experimental data and to in vivo muscle models.  相似文献   
916.
Tree size, survival, and coppicing of micropropagated plantlets, macropropagated cuttings, and seedlings of Eucalyptus grandis Hill ex Maiden were monitored through 57 months in a study in southern Florida to assess propagation options. Two plantlet lines developed by direct micropropagation and orchard open-pollinated seedlings from three ortets were compared in the main study. Rooted cuttings from up to four ramets of each of the three ortets and another ortet were examined in an adjacent supplemental study. Freezes at six and 16 months killed most initial and first-coppice stems to the ground. Most developmental differences in the main study were consistent from ages 2 to 57 months. Propagation by ortet interactions were observed beginning at 21 months, due to the poor performance of seedlings of one ortet after the second freeze. At 57 months, no differences in tree height, DBH, volume, or survival were detected between plantlet lines and between rooted cuttings and plantlets, but seedlings were inferior to plantlets and cuttings. Vegetative propagules had more uniform tree size at every age, with typically less than one-half the variability observed among seedlings. Even though plantlets and cuttings may be more expensive to produce, they have numerous advantages over seedlings for E. grandis plantation establishment in Florida.  相似文献   
917.
Coagulation and fibrinolysis were measured in the portal and peripheral circulation in 15 rabbits after ligation of the superior mesenteric artery. It was found that the local coagulation syndrome in the mesenteric region can be recognized by tests in blood samples taken from the peripheral circulation area.  相似文献   
918.
Ischemia of the rat small intestine lasting 40 min leads to pronounced structural disorders in lipid transport across the enterocytes, reduction in enzymatic activity of the cells and in absorption function, and to the loss of fat with feces. The normalization of the indicated parameters occurs at varying times and ends after 1 month. Fat transport abnormality is marked by an increase in lipid drops in the cavities of the smooth endoplasmic network, appearance of large and numerous matrix lipids, by a greater reduction, as compared to normal, in the membranes of the rough endoplasmic network and lamellar complex in the epithelium of the villi. Accumulation of lipids and retardation of their release from the cytoplasm are determined by incomplete differentiation of the epithelium, which is also combined with a decreased enzymatic activity.  相似文献   
919.
920.
Experiments on E. coli used as a model have revealed that fatty-acid composition is one of the characteristics which determine the viability of bacteria in the air. The viability of microbial cells in the air has been shown to increase with the increase of the pool of cyclopropane acids and the palmitic acid/palmitoleic acid ratio in the cells, irrespective of their genotype and the phase of their growth.  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