全文获取类型
收费全文 | 488398篇 |
免费 | 46007篇 |
国内免费 | 314篇 |
专业分类
534719篇 |
出版年
2018年 | 5534篇 |
2017年 | 5306篇 |
2016年 | 7083篇 |
2015年 | 8807篇 |
2014年 | 10070篇 |
2013年 | 14566篇 |
2012年 | 16401篇 |
2011年 | 16631篇 |
2010年 | 11085篇 |
2009年 | 9811篇 |
2008年 | 14570篇 |
2007年 | 14770篇 |
2006年 | 13991篇 |
2005年 | 13185篇 |
2004年 | 13113篇 |
2003年 | 12583篇 |
2002年 | 12188篇 |
2001年 | 19821篇 |
2000年 | 20138篇 |
1999年 | 15464篇 |
1998年 | 5452篇 |
1997年 | 5642篇 |
1996年 | 5319篇 |
1995年 | 4857篇 |
1994年 | 4705篇 |
1993年 | 4763篇 |
1992年 | 12806篇 |
1991年 | 12828篇 |
1990年 | 12343篇 |
1989年 | 12264篇 |
1988年 | 11325篇 |
1987年 | 10830篇 |
1986年 | 9935篇 |
1985年 | 10216篇 |
1984年 | 8448篇 |
1983年 | 7162篇 |
1982年 | 5268篇 |
1981年 | 4784篇 |
1979年 | 8030篇 |
1978年 | 6285篇 |
1977年 | 5912篇 |
1976年 | 5402篇 |
1975年 | 6250篇 |
1974年 | 6963篇 |
1973年 | 6802篇 |
1972年 | 6223篇 |
1971年 | 5779篇 |
1970年 | 5154篇 |
1969年 | 4970篇 |
1968年 | 4635篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
R F Sturrock 《International journal for parasitology》1973,3(2):165-174
Growth curves, calculated for field populations of B. glabrata, were not materially affected by habitat, altitude or season. A mean growth curve was therefore used to estimate the age-frequency distribution of snails in successive field samples. These data permitted the construction of ecological life tables and the estimation of r, the intrinsic rate of natural increase (or decrease) of the different populations. The calculated values of r were inserted in a simple model of unlimited population growth but the resultant curves poorly represented the observed data. A model for unlimited growth was more satisfactory for pond and marsh populations but, apparently, immigration made it less satisfactory for stream and banana drain populations. Nevertheless, r may still be of value in predicting repopulation rates in certain habitats after a mollusciciding which does not kill the entire snail population. 相似文献
992.
993.
994.
995.
R J Stockert A G Morell I H Scheinberg 《Biochemical and biophysical research communications》1976,68(3):988-993
Oligosaccharide chains of agalactoorosomucoid, α1-acid glycoprotein from which sialic acid and galactose have been sequentially removed, terminate in N-acetylglucosaminyl residues. This protein is rapidly transferred from the circulation into the liver by a route distinct from that previously demonstrated for a number of galactosyl terminating glycoproteins. 相似文献
996.
V I Dontsov 《Biulleten' eksperimental'no? biologii i meditsiny》1987,104(11):618-620
T-cell phenotype that regulates isoproterenol-induced lymphocyte-dependent hyperplasia of mouse salivary glands and conditions of its activation has been investigated. Stimulated Thy-1 and Ly-1-positive cell populations proliferated in the medium supplemented with both interleukin-1 (IL-1) and interleukin-2 (IL-2). The inhibiting population was Thy-1 and Ly-2-positive, proliferating only in IL-2-containing medium. Both regulatory cell properties and the character of their activation are similar to those of lymphocytes that regulate syngeneic mixed lymphocyte culture. The regularities shown may reflect important processes of cell proliferation regulation in multicellular organisms. 相似文献
997.
The inner-dune zone between the villages of Bakkum and Egmond in the North-Holland Dune Reserve is one of the few remaining examples of the semi-natural boundary between the dunes and the polders. For several centuries this area has been used for various purposes, in particular for grazing. Large-scale excavating, especially after about 1900, has encroached upon the dunes. Vegetation and land-use history were studied and a provisional scheme on the vegetation development is presented. Management policies discussed are non-intervention, mowing in order to start natural processes such as rabbit grazing, and the continuation of traditional livestock grazing. Proposals for external management policies were made in order to maintain or enhance the original transition zone, based on comprehensive physical-geographical studies of the whole inner-dune zone. 相似文献
998.
M. T. Garcia J. J. Nieto A. Ventosa F. Ruiz-Berraquero 《Journal of applied microbiology》1987,63(1):63-66
Fifty-eight strains of the moderate halophile Vibrio costicola , including both culture collection strains and freshly isolated strains from solar salterns, were examined for their susceptibility to 10 heavy metal ions by using an agar dilution technique. All strains were sensitive to cadmium, copper, silver, zinc and mercury. This latter ion showed the highest activity even at 0·05 mmol/1 metal concentration. On the other hand, all strains were similarly tolerant to lead, and a great proportion of them were also tolerant to nickel (91%) and chromium (88%). Only 44% and 14% of them showed tolerance to arsenate and cobalt, respectively. The majority of strains (96·4%) were multiply metal-tolerant, with three different metal ion tolerances as the major pattern. 相似文献
999.
1000.
Evidence for the existence of three or more slow phases in the refolding of ribonuclease A and some characteristics of the phases 总被引:1,自引:0,他引:1
The slow refolding kinetics of RNase A have been analyzed, by using a nonlinear least-squares program for deconvoluting the kinetic phases and applying statistical tests for quality of fit. It is found that a minimum of three slow phases are required to fit the kinetic data properly, and this is true whether the method of detection is absorbance of fluorescence. Since the number of phases and the relaxation times for each phase are independent of the method of detection, it is concluded that the same three rate-limiting processes are seen by absorbance and fluorescence. These phases correspond to the XY, CT, and ct phases described in our earlier studies. The fact that fluorescence-detected kinetics are somewhat slower than absorbance-detected kinetics is a trivial effect due not to differences in relaxation times but to the fact that the amplitude of the CT phase is enhanced in fluorescence measurements, at the expense of the faster XY phase, because of intrinsic fluorescence changes associated with the isomerization of proline-93. By use of a new double-jump technique [Schmid, F.X., Grafl, R., Wrba, A., & Beintema, J.J. (1986) Proc. Natl. Acad. Sci. U.S.A. 83, 872], it is shown that proline-93 isomerizes as the rate-limiting step in only one of the three phases, the CT phase, and that this phase involves only 25-30% of the RNase molecules. There is still no indication as to the molecular events that occur in the large, ammonium sulfate dependent XY phase, which is the pathway for formation of the nativelike intermediate. 相似文献