全文获取类型
收费全文 | 5239篇 |
免费 | 766篇 |
国内免费 | 4篇 |
专业分类
6009篇 |
出版年
2022年 | 40篇 |
2021年 | 79篇 |
2020年 | 49篇 |
2019年 | 64篇 |
2018年 | 76篇 |
2017年 | 59篇 |
2016年 | 95篇 |
2015年 | 165篇 |
2014年 | 179篇 |
2013年 | 220篇 |
2012年 | 269篇 |
2011年 | 251篇 |
2010年 | 172篇 |
2009年 | 179篇 |
2008年 | 235篇 |
2007年 | 222篇 |
2006年 | 206篇 |
2005年 | 213篇 |
2004年 | 197篇 |
2003年 | 215篇 |
2002年 | 185篇 |
2001年 | 143篇 |
2000年 | 149篇 |
1999年 | 105篇 |
1998年 | 61篇 |
1997年 | 54篇 |
1996年 | 58篇 |
1995年 | 58篇 |
1994年 | 53篇 |
1993年 | 51篇 |
1992年 | 111篇 |
1991年 | 125篇 |
1990年 | 93篇 |
1989年 | 84篇 |
1988年 | 84篇 |
1987年 | 88篇 |
1986年 | 70篇 |
1985年 | 92篇 |
1984年 | 66篇 |
1983年 | 66篇 |
1982年 | 64篇 |
1981年 | 55篇 |
1980年 | 50篇 |
1979年 | 66篇 |
1978年 | 52篇 |
1977年 | 48篇 |
1976年 | 42篇 |
1974年 | 53篇 |
1972年 | 44篇 |
1970年 | 40篇 |
排序方式: 共有6009条查询结果,搜索用时 11 毫秒
31.
Breast reconstruction by superior gluteal microvascular free flaps without silicone implants 总被引:2,自引:0,他引:2
W W Shaw 《Plastic and reconstructive surgery》1983,72(4):490-501
The author's experience with 10 gluteus maximus myodermal free flap breast reconstructions is reviewed against the current methods of reconstruction using silicone implants, latissimus dorsi flaps, regional skin flaps, and rectus abdominis myodermal flaps. The superior gluteal free flap can achieve a reliable, permanent, and aesthetic reconstruction of the breast without silicone implants. The softness, projection, natural appearance, and patient satisfaction are excellent compared with other methods. It is particularly useful in patients who object to the use of artificial implants, are not suitable for regional flaps, or have disappointing results from previous reconstructions. Technical modifications of the flap design and selection of the recipient vessels are important. 相似文献
32.
Altered proteins with triosephosphate isomerase activity in suppressor-containing strains of Bacillus subtilis 总被引:5,自引:3,他引:2
Suppressor mutations in Bacillus subtilis cause the synthesis of a new protein with the enzymatic activity of l-leucine dehydrogenase and two groups of new proteins with the activity of triosephosphate isomerase. The new isoenzymes of triosephosphate isomerase are separable by zone electrophoresis and differ among themselves in elution behavior upon gel permeation chromatography. One group has an apparent average molecular weight of 120,000 to 135,000, which is more than twice that of the wild-type enzyme. Another group appears to be even higher in molecular weight. These data are consistent with the working hypothesis that the new isoenzymes are produced by extension of growing polypeptide chains through one or more chain-terminating triplets, although other mechanisms resulting in alteration of shapes, charges, or associations of the enzymes are not excluded. 相似文献
33.
Comparative enzymology of the adenosine triphosphate sulphurylases from leaf tissue of selenium-accumulator and non-accumulator plants 总被引:2,自引:0,他引:2 下载免费PDF全文
1. ATP sulphurylases were partially purified (20-40-fold) from leaf tissue of Astragalus bisulcatus, Astragalus racemosus (selenium-accumulator species) and Astragalus hamosus and Astragalus sinicus (non-accumulator species). Activity was measured by sulphate-dependent PP(i)-ATP exchange. The enzymes were separated from pyrophosphatase and adenosine triphosphatase activities. The properties of the Astragalus ATP sulphurylases were similar to the spinach enzyme. 2. The ATP sulphurylases from both selenium-accumulator and non-accumulator species catalysed selenate-dependent PP(i)-ATP exchange; selenate competed with sulphate. The ratio of V(selenate)/V(sulphate) and K(m)(selenate)/K(m)(sulphate) was approximately the same for the enzyme from each species. 3. Sulphate-dependent PP(i)-ATP exchange was inhibited by ADP, chlorate and nitrate. The kinetics of the inhibition for each enzyme were consistent with an ordered reaction mechanism, in which ATP is the first substrate to react with the enzyme and PP(i) is the first product released. 4. Synthesis of adenosine 5'-[(35)S]sulphatophosphate from [(35)S]sulphate was demonstrated by coupling the Astragalus ATP sulphurylases with Mg(2+)-dependent pyrophosphatase; the reaction was inhibited by selenate. An analogous reaction using [(75)Se]selenate as substrate could not be demonstrated. 相似文献
34.
35.
36.
Fatty Acid Composition of Escherichia coli as a Possible Controlling Factor of the Minimal Growth Temperature. 总被引:3,自引:1,他引:2
Shaw, Maxwell K. (University of California, Davis), and John L. Ingraham. Fatty acid composition of Escherichia coli as a possible controlling factor of the minimal growth temperature. J. Bacteriol. 90:141-146. 1965.-If Escherichia coli ML30 is shifted from 37 to 10 C during exponential growth in glucose minimal medium, a 4.5-hr lag results. During this lag, the proportion of unsaturated fatty acids increases in the cellular lipids. However, the adjustment of the fatty acid composition does not appear to be prerequisite to growth at 10 C. If shifts are made to 10 C into minimal medium containing glucose after starvation for glucose at 37 C for 0.5 and 16 hr, the lag periods at 10 C are 4.5 and 6 hr, respectively. Withholding glucose during the lag periods does not affect the duration of the lag periods, but no change in fatty acid composition occurs if glucose is not present. Supplementing the medium with glucose after the lag period permits immediate growth at 10 C; however, the fatty acid composition is still typical of cells grown at 37 C. It is concluded that the fatty acid composition of cells does not determine the minimal temperature of growth. 相似文献
37.
38.
Feces from a specimen of Tamandua tetradactyla (Linn.) from Portel, Pará State, north Brazil, contained two different coccidial oocysts; one identified as Eimeria tamanduae Lainson 1968, and the other as a new species, described here as Eimeria corticulata n. sp. Oocysts of E. corticulata are ellipsoidal, 37.4 x 30.4 (31.2-43.7 x 23.7-35.0) microns, shape index (length/width) 1.2 (1.0-1.5). Oocyst wall 2.5-3.7 microns thick and composed of two layers; an outer thick, brown-yellow one with radial striations, and a thin inner smooth one: no visible micropyle. Oocyst residuum a large globule of about 10.7 x 10.3 microns, usually accompanied by a number of smaller attached globules. Sporocysts ellipsoidal, 21.0 x 11.0 (20.0-22.5 x 10.0-12.5) microns, with a conspicuous Stieda body; shape index 1.9 (1.6-2.2). Sporocyst residuum a small number of scattered granules: sporozoites 18.7 x 5.0 microns, with a large posterior refractile body. Eimeria zygodontomyis n. sp. is described in feces from Zygodontomys lasiurus (Lund) from the Serra dos Carajás, Pará. Oocysts ellipsoidal to cylindrical, 16.5 x 12.0 (13.7-18.7 x 11.2-12.3) microns, shape index 1.4 (1.2-1.5). Wall colorless, smooth, single-layered and about 0.6 micron thick: no micropyle. No oocyst residuum, but a polar granule of about 1.8 x 1.0 microns is sometimes present. Sporocysts ellipsoidal, 8.4 x 5.5 (7.5-8.7 x 5.0-6.2) microns, shape index 1.5 (1.4-1.7), with a thin colorless wall and a delicate Stieda body. Sporozoites enclose a compact residuum of about 2.5 x 3.7 microns. 相似文献
39.