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   227612篇
  免费   15294篇
  国内免费   51篇
  242957篇
  2021年   1832篇
  2018年   3184篇
  2017年   3103篇
  2016年   3784篇
  2015年   3369篇
  2014年   4647篇
  2013年   6555篇
  2012年   7854篇
  2011年   8325篇
  2010年   5926篇
  2009年   5035篇
  2008年   7407篇
  2007年   7711篇
  2006年   7365篇
  2005年   6892篇
  2004年   7017篇
  2003年   6712篇
  2002年   6694篇
  2001年   9316篇
  2000年   8992篇
  1999年   7033篇
  1998年   2164篇
  1997年   1983篇
  1996年   1858篇
  1992年   5484篇
  1991年   5700篇
  1990年   5674篇
  1989年   5644篇
  1988年   5239篇
  1987年   4873篇
  1986年   4454篇
  1985年   4692篇
  1984年   3710篇
  1983年   3036篇
  1982年   2024篇
  1981年   1735篇
  1980年   1733篇
  1979年   3349篇
  1978年   2584篇
  1977年   2382篇
  1976年   2341篇
  1975年   2832篇
  1974年   3122篇
  1973年   3096篇
  1972年   2751篇
  1971年   2606篇
  1970年   2213篇
  1969年   2159篇
  1968年   2033篇
  1967年   1800篇
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
81.
Peak area matching and linear regression were used to quantify eight chlorinated pesticides and polychlorinated biphenyls (as Aroclor 1260) in human serum. There are no statistically significant differences in data obtained by these two quantifying techniques which were indicated by the paired t-test. For chlorinated pesticides, p = 0.053-0.62, and for polychlorinated biphenyls (as Aroclor 1260), p = 0.64. Analyte residues for the chlorinated pesticides ranged from 0.5 ppb for hexachlorobenzene (HCB) to 186 ppb for dichlorodiphenyldichloroethylene (DDE). Analyte residues for the polychlorinated biphenyls (as Aroclor 1260) ranged from 5-114 ppb. The absolute mean percent difference between the two quantifying techniques ranged from 0.06% for DDE to 8.06% for dieldrin (HEOD) among the chlorinated pesticides. The absolute mean percent difference between the two quantifying techniques for the polychlorinated biphenyls (as Aroclor 1260) was 3.4%. Peak area matching and linear regression were found to be comparable for quantifying these environmental residues in serum when the following conditions apply: 1) the concentration of the chlorinated pesticides is greater than or equal to 0.5 ppb (e.g., HCB, hexachlorocyclohexane (HCCH), oxychlordane (OC), heptachlor epoxide (HE), transnonachlor (TN), HEOD, and dichlorodiphenyltrichloroethane (DDT); 2) the concentration of the chlorinated pesticide is greater than or equal to 3 ppb (e.g., DDE); and 3) the total concentration of polychlorinated biphenyls (e.g., as Aroclor 1260) is greater than or equal to 5 ppb.  相似文献   
82.
[2-14C] leucine, [1-14C] alanine, [1-14C] glucose, [1-14C] lactate and [1-14C] pyruvate utilization in the protein synthesis has been studied in vivo at early stages of postnatal development of piglets. It has been established, that during the first 24 hours after birth the protein synthesis intensity, judging by [2-14C] leucine incorporation, in liver, skeletal muscle, duodenal wall and subcutaneous tissue of piglets increases 5, 7, 6.5 and 2.1 times respectively. At the age of 1-2 h the radioactive carbon incorporation from [1-14C] glucose into the brain proteins is more pronounced than into the proteins of liver and skeletal muscle. During the first days of life the intensity of the label incorporation from [1-14C] glucose into liver and skeletal muscle proteins of piglets is enhanced, whereas in brain it remains at the same level. The degree of 14C carbon incorporation from [1-14C]-alanine, [1-14C] pyruvate and [1-14C] lactate into the liver and skeletal muscle proteins of 5-days-old piglets is approximately the same, 14C substrates of protein synthesis in brain and subcutaneous adipose tissue having some peculiarities.  相似文献   
83.
Proteases with the thrombolytic activity were studied in 212 strains of actinomycetes isolated from different soils of the Soviet Union. The cultures belonged to the genera Micromonospora, Nocardia and Streptomyces. Proteases were synthesized by 41% of the studied actinomycetes and some of their strains completely dissolved in vitro artificially obtained blood thrombi within 120-240 min. In the Streptomyces genus, more active strains were found in the groups Flavus, Fradia and Globisporus. The groups Olivaceus, Violaceus and Viridis had less active strains.  相似文献   
84.
The infection of Planorbarius banaticus with sporocysts of Cotylurus cornutus is accompanied by an increase in aldolase activity of molluscs' haemolymph of 1.2 fold. In solutions of nitroammofoska (0.1, 1 and 10 mg/1) the activity of this ferment in infected individuals increases much higher than in non-infected ones. This results in fast carbohydrate expenditures by molluscs, intermediate hosts of trematodes, and their death from exhaustion.  相似文献   
85.
Infravesical obstruction in 300 male patients was determined by prostatic sclerosis (PS). PS is a polyetiological disease developing more frequently as a result of prostatitis, autoimmune, allergic and congestive factors. Sclerosis and shriveling of the gland cause topographo-anatomic changes in the infravesical area, well revealed during a combined roentgeno-urological study. Direct signs of PS are the following: stenosis, deformity and shortening of the prostatic part of the urethra, a high position of the lower outline of the bladder resembling braces over the public symphysis; indirect signs: change of the bladder shape, megacyst, trabecular mucosa and diverticulosis, congestion in the upper urinary tracts, uni- or bilateral urethero-hydronephrosis.  相似文献   
86.
The effects of corticotropin-releasing hormone (CRH) injected into the dorsal neostriatum on the open-field and shuttle-box behavior were studied in rats with high (Koltushi high avoidance, KHA) and low (Koltushi low avoidance, KLA) capability for avoidance learning. The effects of this hormone on the behavior of these rat strains were different. In KLA rats with passive strategy of behavior the CRH injection led to a rapid locomotor activation in the open field, while the rats with active behavioral strategy (KHA) reacted to the injection by a significant decrease in locomotion and change for the passive mode of behavior. The same CRH effects on locomotion were obtained in the shuttle-box experiments. Moreover, in the KLA rats the neurohormone injection resulted in an improvement of avoidance learning in contrast to the KHA rats, in which CRH substantially impaired avoidance learning. The obtained evidence is discussed in terms of the important role of striatal CRH in the choice of behavioral strategy in stress.  相似文献   
87.
X-IRRADIATION of mammalian cells in culture yields a survival curve of the threshold type (for review see ref. 1). It isjnter-esting to ask how one can enhance the radiation response by small changes of the physical environment of the cells, as can be done chemically, for example, by incorporation of 5-bromo-deoxyuridine into DNA1,2. Elevation of the temperature is a likely prospect for enhancement of radiosensitivity for the following reasons. It is known that proteins are heat labile and that temperature sensitive mutants of bacteria and phage can be obtained for many different enzymes3 which are operative at 37° C but not at 42° or 43°C. For example4, DNA polymerase is reversibly temperature sensitive; it is rendered inoperative above 42°C, but will be functional again when the temperature is lowered. It is not unreasonable to expect that temperature sensitive mutations for many enzymes occur frequently and that the use of temperatures somewhat higher than the normal range at which the cells grow might disclose sensitivities for specific enzymes in normal cells of higher organisms.  相似文献   
88.
89.
90.
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