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   1078554篇
  免费   118381篇
  国内免费   863篇
  1197798篇
  2018年   9328篇
  2016年   12706篇
  2015年   17819篇
  2014年   20832篇
  2013年   29748篇
  2012年   33112篇
  2011年   33556篇
  2010年   22733篇
  2009年   20883篇
  2008年   29760篇
  2007年   30750篇
  2006年   28993篇
  2005年   28070篇
  2004年   27873篇
  2003年   26773篇
  2002年   26026篇
  2001年   48133篇
  2000年   48734篇
  1999年   38924篇
  1998年   13877篇
  1997年   14477篇
  1996年   13490篇
  1995年   12750篇
  1994年   12387篇
  1993年   12295篇
  1992年   31997篇
  1991年   31113篇
  1990年   30378篇
  1989年   29608篇
  1988年   27820篇
  1987年   26047篇
  1986年   24369篇
  1985年   24383篇
  1984年   20283篇
  1983年   17207篇
  1982年   13358篇
  1981年   12125篇
  1980年   11230篇
  1979年   18970篇
  1978年   15038篇
  1977年   13659篇
  1976年   12587篇
  1975年   14055篇
  1974年   15281篇
  1973年   15117篇
  1972年   13671篇
  1971年   12525篇
  1970年   10742篇
  1969年   10521篇
  1968年   9578篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
931.
932.
Fort Greely, Alaska has an extensive complex of weapon training and testing areas located on lands withdrawn from the public domain under the Military Lands Withdrawal Act (PL106-65). The Army has pledged to implement a program to identify possible munitions contamination. Because of the large size (344,165,000 m2) of the high hazard impact areas, characterization of these constituents will be difficult. We used an authoritative sampling design to find locations most likely to contain explosives-residues on three impact areas. We focused our sampling on surface soils and collected multi-increment and discrete samples at locations of known firing events and from areas on the range that had craters, pieces of munitions, targets, or a designation as a firing point. In the two impact areas used primarily by the Army, RDX was the most frequently detected explosive. In the impact area that was also used by the Air Force, TNT was the most frequently detected explosive. Where detected, the explosives concentrations generally were low (<0.05 mg/kg) except in soils near low-order detonations, where the explosive-filler was in contact with the soil surface. These low-order detonations potentially can serve as localized sources for groundwater contamination if positioned in recharge areas.  相似文献   
933.
934.
Pst I RFLP close to the LDL receptor gene.   总被引:2,自引:1,他引:1       下载免费PDF全文
  相似文献   
935.
ABSTRACT. Diplonevra mortimeri sp.nov. and D.watsoni. sp.nov. are described from specimens caught at Nasutitermitinae termite colonies in Sulawesi. The female of both species has a remarkable pre-oviposition behaviour in which she lures a worker termite into following her away from the colony. She then oviposits in the termite's abdomen. Pupation takes place within the remains of the host's abdomen. Both species only mature a single egg at a time. The female probably guards the comatose host termite during the period of larval development. The morphology of the male hypopygia of the new species allows reinterpretation of the peculiar anal tube in typical male Diplonevra. Furthermore the suggested homologies reinforce the view that the epandrium (tergite 9) has not been replaced by a periandrium (fused gonocoxites) in the Cyclorrhapha and consequently the latter cannot be derived from the Empidoidea.  相似文献   
936.
Concentrated adult erythrocyte suspensions were subjected to low amplitude oscillatory shear in a Weissenberg rheogoniometer equipped with a cone-and-plate assembly. The dynamic viscoelastic properties of the suspension were measured over a broad range of frequency by a numerical solution that accounted for fluid inertia. Variation of shear amplitude and cell volume percent, and comparison of buffered saline, plasma, and dextran as suspending media showed that the cellular elements had undergone small bending and shearing deformations. Studies of normal adult erythrocytes, hypotonically swollen cells, temperature-altered cells, and erythrocyte ghosts suggested that the method was evaluating membrane material properties. The normal membrane was found to exhibit a shear rate dependent elastic modulus that increased by more than a factor of 20 over a frequency range from 0.0076 Hz to 60 Hz. The membrane viscosity showed a substantial drop with frequency indicative of a frequency thinning phenomenon. At high frequency of deformation the viscous response of normal erythrocytes was no longer indicative of a membrane property due to the dominant influence of the internal hemoglobin solution. The studies generally supported the ability of the method to quantify relative membrane material properties and detect changes in membrane structure.  相似文献   
937.
938.
Summary A male fetus of a pregnancy known to be at risk for X-linked mental retardation with fragile site Xq27 was found to be affected by demonstrating the marker X-chromosome in five of 180 (2.8%) of metaphases derived from amniocytes cultured in medium 199. The results were confirmed in fetal lymphocytes (25 of 86 metaphases, i.e. 29%), and fetal fibroblasts (five of 100 metaphases when cultured in medium 199, and 14 of 100 after exposure to methotrexate for 43 h).This work was supported in part by a research grant from the Deutsche Forschungsgemeinschaft  相似文献   
939.
Several isoforms of apoprotein A-I [apoA-I], the major apoprotein of high density lipoproteins [HDL], have been described. We compared the in vivo and in vitro properties of normal human apoA-I with those of apoA-I [Lys107----0]. Fluorescence and circular dichroic spectra showed that deletion of Lys107 decreases apoprotein self-association. In vivo metabolic studies in the rat indicated that the interaction of apoA-I [Lys107----0] with HDL was lower than normal. We conclude that deletion of Lys107 results in a reorganization of the apoprotein structure that decreases its potential to form hydrophobic associations.  相似文献   
940.
The receptor for asialoglycoproteins was isolated from murine liver and was purified by means of biospecific chromatography on sepharose-Asialo-orosomucoid. The obtained receptor with an absorption maximum at 277 nm binds to the nonreducing terminal galactosyl residues of glycoproteins similar to the receptors from liver of other mammalians. The interaction between this receptor and desialylated glycoproteins requires the presence of calcium. The dependence of specific binding on the concentration of [125I]acialo-orosomucoid used as a ligand gives a saturating curve. The dissociation constant for the receptor-ligand complex is 0.4 X 10(-9) M. Similar to asialo-orosomucoid, the receptor binds the p-aminophenyl-beta-D-galactopyranoside derivatives of bovine serum albumin, ovalbumin and acid alpha-glucosidase synthesized by us earlier. Possible use of the asialoglycoprotein receptor as a highly specific carrier transporting the modified acid alpha-glucosidase to hepatocyte lysosomes is discussed.  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