全文获取类型
收费全文 | 7719篇 |
免费 | 933篇 |
国内免费 | 4篇 |
出版年
2021年 | 73篇 |
2020年 | 61篇 |
2019年 | 87篇 |
2018年 | 90篇 |
2017年 | 84篇 |
2016年 | 123篇 |
2015年 | 248篇 |
2014年 | 247篇 |
2013年 | 276篇 |
2012年 | 398篇 |
2011年 | 418篇 |
2010年 | 234篇 |
2009年 | 214篇 |
2008年 | 348篇 |
2007年 | 394篇 |
2006年 | 347篇 |
2005年 | 335篇 |
2004年 | 320篇 |
2003年 | 302篇 |
2002年 | 330篇 |
2001年 | 197篇 |
2000年 | 197篇 |
1999年 | 158篇 |
1998年 | 100篇 |
1997年 | 92篇 |
1996年 | 80篇 |
1995年 | 87篇 |
1994年 | 78篇 |
1993年 | 84篇 |
1992年 | 111篇 |
1991年 | 134篇 |
1990年 | 111篇 |
1989年 | 118篇 |
1988年 | 131篇 |
1987年 | 96篇 |
1986年 | 92篇 |
1985年 | 102篇 |
1984年 | 138篇 |
1983年 | 91篇 |
1982年 | 96篇 |
1981年 | 89篇 |
1980年 | 70篇 |
1979年 | 88篇 |
1978年 | 80篇 |
1977年 | 71篇 |
1976年 | 70篇 |
1974年 | 87篇 |
1973年 | 79篇 |
1971年 | 64篇 |
1968年 | 58篇 |
排序方式: 共有8656条查询结果,搜索用时 31 毫秒
21.
Bitches exhibited a characteristic arborization pattern of the fluid from the anterior vagina during pro-oestrus and oestrus. These changes were monitored together with conventional vaginal cytology and plasma oestrogen and progestagen concentrations. A classical ferning pattern, similar to that seen in bovine cervical mucus at oestrus, occurred after the peak in plasma oestrogen concentrations. Ferning was most intense after the second peak of cornification of vaginal epithelial cells. It is suggested that a 'Ferning Index', when combined with conventional vaginal cytology, can be of use in determining the optimum mating time in the bitch. 相似文献
22.
23.
Superoxide dismutase activity and glutathione concentration during the calcium-induced differentiation of Physarum polycephalum microplasmodia 总被引:2,自引:0,他引:2
C Nations R G Allen A K Balin R J Reimer R S Sohal 《Journal of cellular physiology》1987,133(1):181-186
Microplasmodia of Physarum polycephalum differentiate into spherules when the CaCl2 concentration of their nutrient medium is increased to 54mM (high-calcium). The salts starvation medium routinely used to induce differentiation contains 8mM CaCl2. This medium will not induce spherulation in the absence of a calcium salt; no other metal is essential. High-calcium also induces the spherulation of a strain of Physarum that had not been previously observed to spherulate. The striking increase in superoxide dismutase activity (SOD) and the decrease in glutathione concentration (GSH) that are characteristic of salts-induced spherulation do not occur in salts media containing high-calcium. In the absence of calcium, no significant change in SOD is observed and very little change in GSH occurs. The immediate effect of the oxidative stress associated with spherulation may be the release of calcium stores into the cytosol. The parameters modulating this stress are, in turn, sensitive to exogenous calcium concentrations. 相似文献
24.
Thyrotropin releasing hormone (TRH) administered both intraventricularly and parenterally suppressed stress induced eating (using the mild tail pinch model) in a dose related manner. This suppression was partially reversed by intraventricular administration of the long acting synthetic enkephalin analog, D-Ala-Met-Enkephalin (p < 0.01). Preliminary data suggests that the naturally occurring metabolic breakdown product of TRH, histidyl-proline-diketopiperazine, may be the active substance with TRH acting as a pro-hormone. The TRH effect was present in hypophysectomized animals showing that the TRH-induced decrease in food ingestion was not secondary to an increase in thyrotropin or thyroid hormones. TRH did not alter blood glucose levels. Our data is compatible with a possible physiological role for TRH, as a peptidergic mediator of satiety acting as a direct antagonist of the lateral hypothalamic of satiety acting as a direct antagonist of the lateral hypothalamic enkephalin-mediated feeding center. 相似文献
25.
A series of eight novel, highly modified mono-, di- and trisaccharide derivatives, each containing an iminoalditol moiety, has been synthesized in the quest for potential heparanase inhibitors. 相似文献
26.
Polymerase chain reaction amplification products separated on rehydratable polyacrylamide gels and stained with silver 总被引:16,自引:0,他引:16
Separation of polymerase chain reaction (PCR) amplification of specific fragment length polymorphisms was carried out on rehydratable polyacrylamide gels on a horizontal flat slab system. A discontinuous sulfate-borate buffer system was employed on 5-8% T gels crosslinked with 3.5% C. Samples were diluted in leading sulfate ion buffer at 1/10 the ionic strength of the separating gel buffer and placed directly onto the surface of the rehydrated gels in 0.5-10 microliters volumes. The trailing ion and counterion were contained in a gel plug and placed directly onto the anodal and cathodal ends of the gel, and the electrodes placed directly onto the surface of the gel plugs. Filter paper wicks, soaked in diluted leading ion buffer, were placed along each side to lower the ionic strength of the edges, thereby increasing mobility at the edge and thus preventing smile effects. The gel-gel contact of the plug and separating gel prevent the production of a junction potential which occurs between dissimilar materials such as a paper wick and the gel. Ten- to 20-cm separations were carried out from 2-5 h, respectively, and resolution in the 20 cm system was 1.6-4 bp (base pairs) between 100 and 500 bp, 4-7 bp between 500 and 1000 bp, 12-20 bp between 1000 and 2000 bp and about 50 bp between 2000 and 3000 bp. Between 3000 and 4000 bp, resolution fell off to +/- 100 bp. Sensitivity, using a silver stain, indicated that one could readily distinguish less than 10 pg of DNA per mm width on the gels.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
27.
28.
Jeffrey Pomerance Richard Johnson Shoba Kagal Philip Brooks Malcolm Margolin Arthur Allen 《The Western journal of medicine》1980,133(4):289-291
Recently, there has been increased interest in the influence of maternal prenatal nutrition on the course and outcome of pregnancy. Evidence has accumulated that a woman''s weight before pregnancy and the weight gained during pregnancy directly affect infant birth weight, incidence of neonatal mortality, and growth and development of the infant during the first year of life. Although recent recommendations for weight gain in pregnancy have been liberalized, a survey of 195 pregnant women who had prenatal visits in both clinic and private offices showed deficiencies in their understanding of the subject. Some 37 percent of women believed they should gain 20 pounds (9 kg) or less during pregnancy. Eight percent admitted to dieting before at least one antenatal visit and 54 percent thought their doctor would not be concerned about too little weight gained during pregnancy. This suggests that many women and some doctors are still ignorant of current concepts of proper nutrition during pregnancy. Apparently, increased lay and professional educational efforts are needed. 相似文献
29.
30.
Application of carrier testing to genetic counseling for X-linked agammaglobulinemia. 总被引:6,自引:4,他引:2 下载免费PDF全文
R. C. Allen R. G. Nachtman H. M. Rosenblatt J. W. Belmont 《American journal of human genetics》1994,54(1):25-35
Bruton X-linked agammaglobulinemia (XLA) is a phenotypically recessive genetic disorder of B lymphocyte development. Female carriers of XLA, although asymptomatic, have a characteristic B cell lineage-specific skewing of the pattern of X inactivation. Skewing apparently results from defective growth and maturation of B cell precursors bearing a mutant active X chromosome. In this study, carrier status was tested in 58 women from 22 families referred with a history of agammaglobulinemia. Primary carrier analysis to examine patterns of X inactivation in CD19+ peripheral blood cells (B lymphocytes) was conducted using quantitative PCR at the androgen-receptor locus. Obligate carriers of XLA demonstrated > 95% skewing of X inactivation in peripheral blood CD19+ cells but not in CD19- cells. Carrier status for mothers of isolated affected males could be assessed in 10 of 11 families: 7 women showed skewing, and 3 did not. Five carriers were found in six families in which there were no living affected males. Among all those tested, one individual's carrier status was considered to be indeterminate and five women were noninformative for the carrier test. Results obtained by the carrier test were congruent with linkage analysis (where applicable) using the RFLPs DXS178 and DXS94 and two newly developed polymorphic microsatellite markers, DXS178CA and DXS101AAT. Refinements in techniques for primary carrier testing and genetic mapping of XLA now make possible an ordered approach to diagnosis, prenatal diagnosis, and genetic counseling. 相似文献