全文获取类型
收费全文 | 19319篇 |
免费 | 1740篇 |
国内免费 | 10篇 |
出版年
2022年 | 141篇 |
2021年 | 216篇 |
2020年 | 155篇 |
2019年 | 202篇 |
2018年 | 251篇 |
2017年 | 247篇 |
2016年 | 347篇 |
2015年 | 723篇 |
2014年 | 796篇 |
2013年 | 1000篇 |
2012年 | 1210篇 |
2011年 | 1268篇 |
2010年 | 827篇 |
2009年 | 766篇 |
2008年 | 1068篇 |
2007年 | 1143篇 |
2006年 | 1086篇 |
2005年 | 1092篇 |
2004年 | 1072篇 |
2003年 | 880篇 |
2002年 | 882篇 |
2001年 | 300篇 |
2000年 | 248篇 |
1999年 | 271篇 |
1998年 | 286篇 |
1997年 | 172篇 |
1996年 | 146篇 |
1995年 | 130篇 |
1994年 | 156篇 |
1993年 | 135篇 |
1992年 | 176篇 |
1991年 | 170篇 |
1990年 | 142篇 |
1989年 | 170篇 |
1988年 | 133篇 |
1987年 | 150篇 |
1986年 | 132篇 |
1985年 | 153篇 |
1984年 | 137篇 |
1983年 | 127篇 |
1982年 | 147篇 |
1981年 | 130篇 |
1980年 | 106篇 |
1979年 | 104篇 |
1978年 | 93篇 |
1977年 | 108篇 |
1976年 | 77篇 |
1974年 | 107篇 |
1973年 | 88篇 |
1972年 | 80篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
51.
The measurement of the ATP content of fresh semen is as accurate as the estimation of sperm motility by conventional methods in discriminating between semen of fertile versus subfertile men. The ATP content of frozen thawed donor semen is correlated with the probability of conception per cycle of insemination. Exact quantification of cytotoxic sperm antibodies in serum is possible with the adenosine-triphosphate-release-cytotoxicity test, since measurement is free of the bias of microscopic examination. The procedure has been simplified by testing only one serum dilution and calculating the ‘sperm toxicity index’. 相似文献
52.
53.
Frank Josef Mller Oliver Zierau Torsten Hertrampf Anja Bliedtner Patrick Diel Günter Vollmer 《The Journal of steroid biochemistry and molecular biology》2009,113(3-5):296-303
Isoflavones (ISOs) are bioactive food ingredients of the traditional East Asian diet and currently discussed as alternatives to classical hormone replacement therapies and for reducing the prevalence of hormone-dependent cancers. Although there are many studies on ISOs, not much is known about their long-term effects.Therefore, we performed an animal experiment analyzing the effects of three different diets: a phytoestrogen-free diet, a diet supplemented with genistein (700 μg/g diet) and an ISO-high diet (232 μg daidzein and 240 μg genistein/g) at two distinct time points, juvenile (21 days) and adult (97 days). Exposure started prior to mating of the parents and throughout the life of the offspring.We observed a stronger increase of uterine wet weights in juvenile offspring with genistein exposure (1018 ± 350 mg/kg BW) than with ISO-high diet (497 ± 133 mg/kg BW). Whereas the expression of proliferation related genes (PCNA; Ki67; IGF-1; IGF-1R), analyzed by real-time-qPCR and Western blot, were significantly down-regulated in juvenile animals exposed to genistein. Additionally, genistein exposure led to estrogenic responses, observed upon increase of complement C3 and decrease of estrogen receptors gene expressions, while the exposure to ISO-high diet did not show these effects.In conclusion, both the time point on which phytoestrogen exposure starts together with the composition of the ingested phytoestrogen containing diet are of great importance for the biological response of the offspring. 相似文献
54.
Fine structure of the ion transporting epithelium of the neck organ in the brine shrimp (Artemia salina) nauplius is described. The neck organ is a dome-like gland situated atop the cephalothorax of the larva and is composed of 50 to 60 cuboidal epithelial cells. These cells possess many of the characteristics of salt-secretory cells from other tissues. They contain many mitochondria and exhibit a high degree of plasma membrane elaboration. This membrane amplification takes two forms; the apical plasmalemma is infolded into irregular loops, while the basal and lateral membranes penetrate the cytoplasm in the form of branching sinusoids. The labyrinth of tubular reticulum thus formed fills most of the cell volume. Mitochondria in the labyrinth are often in intimate contact with these tubular membranes and regular arrays of parallel mitochondria with constricted intervening sinusoids are often observed. Other organelles including Golgi complexes, multivesicular bodies, and rough endoplasmic reticulum are also numerous, particularly in the narrow rim of cytoplasm which lies between the apical infolds and the labyrinth. Yolk platelets and glycogen fields are conspicuous in the basal perinuclear regions of the cells. 相似文献
55.
56.
57.
Frank D. Gunstone Janet A. Holliday Charles M. Scrimgeour 《Chemistry and physics of lipids》1977,20(4):331-335
The crystalline material which separates from Argemone mexicana seed oil is a mixture of 9-and 11-oxo-octacosanoic and 11-oxotriacontanoic acids. 相似文献
58.
Berthold Lausen Torsten Hothorn Frank Bretz Martin Schumacher 《Biometrical journal. Biometrische Zeitschrift》2004,46(3):364-374
The identification and assessment of prognostic factors is one of the major tasks in clinical research. The assessment of one single prognostic factor can be done by recently established methods for using optimal cutpoints. Here, we suggest a method to consider an optimal selected prognostic factor from a set of prognostic factors of interest. This can be viewed as a variable selection method and is the underlying decision problem at each node of various tree building algorithms. We propose to use maximally selected statistics where the selection is defined over the set of prognostic factors and over all cutpoints in each prognostic factor. We demonstrate that it is feasible to compute the approximate null distribution. We illustrate the new variable selection test with data of the German Breast Cancer Study Group and of a small study on patients with diffuse large B‐cell lymphoma. Using the null distribution for a p‐value adjusted regression trees algorithm, we adjust for the number of variables analysed at each node as well. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
59.
F J Klinz R Seifert I Schwaner H Gausepohl R Frank G Schultz 《European journal of biochemistry》1992,207(1):207-213
Specific antibodies against rap1A and rap1B small GTP-binding proteins were generated by immunization of rabbits with peptides derived from the C-terminus of the processed proteins. Immunoblot analysis of membranes from several mammalian cell lines and human thrombocytes with affinity-purified antibodies against rap1A or rap1B demonstrated the presence of multiple immunoreactive proteins in the 22-23 kDa range, although at strongly varying levels. Whereas both proteins were present in substantial amounts in membranes from myelocytic HL-60, K-562 and HEL cells, they were hardly detectable in membranes from lymphoma U-937 and S49.1 cyc- cells. Membranes from human thrombocytes and 3T3-Swiss Albino fibroblasts showed strong rap1B immunoreactivity, whereas rap1A protein was present in much lower amounts. In the cytosol of HL-60 cells, only small amounts of rap1A and rap1B proteins were detected, unless the cells were treated with lovastatin, an inhibitor of hydroxymethylglutaryl-coenzyme A reductase, suggesting that both proteins are isoprenylated. By comparison with recombinant proteins, the ratio of rap1A/ras proteins in membranes from HL-60 cells was estimated to be about 4:1. An antiserum directed against the C-terminus of rap2 reacted strongly with recombinant rap2, but not with membranes from tested mammalian cells. In conclusion, rap1A and rap1B proteins are distributed differentially among membranes from various mammalian cell types and are isoprenylated in HL-60 cells. 相似文献
60.
Results were compared between the latex paint and compressed air methods for determining total vessel lengths, and between the sectioning and maceration methods for determining vessel diameters. The minimum, mean, median, and maximum vessel diameters were less with the sectioning method than with the maceration technique. Vessel diameter distributions were always nonnormal and had roughly similar patterns with the two techniques, but were statistically different from one another. In all six species where the paint and air methods for determining vessel length were compared, both methods showed a similar skewed vessel length distribution, with many short vessels and few long ones. Although there was no consistent pattern to the difference in results with these two methods, the vessel length frequency distributions were statistically different from one another. With the paint method, many vessels, especially many of the narrowest ones, were not paint-filled at the paint infusion port. The air method utilized the paint method, in part, and, in addition, is based upon the incorrect assumption that all vessels in the stem are the same diameter. Both techniques tended to exclude vessel lengths of the narrowest vessels. However, the narrow vessels, although numerous, contributed an insignificant amount to the total theoretical hydraulic conductance in stems. 相似文献