全文获取类型
收费全文 | 36566篇 |
免费 | 2700篇 |
国内免费 | 147篇 |
出版年
2023年 | 306篇 |
2022年 | 516篇 |
2021年 | 950篇 |
2020年 | 727篇 |
2019年 | 796篇 |
2018年 | 1328篇 |
2017年 | 1055篇 |
2016年 | 1465篇 |
2015年 | 1794篇 |
2014年 | 1907篇 |
2013年 | 2575篇 |
2012年 | 3040篇 |
2011年 | 3062篇 |
2010年 | 1835篇 |
2009年 | 1476篇 |
2008年 | 2163篇 |
2007年 | 2142篇 |
2006年 | 1946篇 |
2005年 | 1549篇 |
2004年 | 1487篇 |
2003年 | 1315篇 |
2002年 | 1136篇 |
2001年 | 680篇 |
2000年 | 730篇 |
1999年 | 483篇 |
1998年 | 282篇 |
1997年 | 211篇 |
1996年 | 201篇 |
1995年 | 177篇 |
1994年 | 158篇 |
1993年 | 143篇 |
1992年 | 181篇 |
1991年 | 174篇 |
1990年 | 134篇 |
1989年 | 111篇 |
1988年 | 107篇 |
1987年 | 86篇 |
1986年 | 70篇 |
1985年 | 82篇 |
1984年 | 76篇 |
1983年 | 61篇 |
1982年 | 68篇 |
1981年 | 60篇 |
1980年 | 50篇 |
1979年 | 55篇 |
1978年 | 53篇 |
1976年 | 37篇 |
1975年 | 42篇 |
1974年 | 32篇 |
1973年 | 37篇 |
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
131.
Synthesis of hydroxy fatty acids from 4, 7, 10, 13, 16, 19-[1-14C] docosahexaenoic acid by human platelets 总被引:2,自引:0,他引:2
Human platelets incubated in the presence of 54 microM [1-14C]22:6 produced hydroxydocosahexaenoic acid (HDHE) at about half the rate with which 12-hydroxy-5,8,10,14-eicosatetraenoic acid is produced from [1-14C]arachidonic acid. More than 90% of the radioactivity in HDHE was distributed among two major isomers, 14-HDHE and 11-HDHE. The production of HDHEs was unaffected by indomethacin but completely inhibited by 5,8,11,14-heneicosatetraynoic acid, which suggests that the hydroxy fatty acids are produced by lipoxygenase. The proportions of HDHE isomers varied with the concentration of 22:6. The ratio 14-HDHE/11-HDHE was higher at 6.8 microM 22:6 than when platelets were incubated with 54 microM 22:6. It is suggested that the amounts of these isomers produced will depend both on the availability of 22:6 as well as by competition of this acid with other acids for lipoxygenase. 相似文献
132.
J. Fernandez-Piqueras A. Rodriguez Campos C. Sentis Castaño E. Rojo Garcis 《Genetica》1983,61(1):9-12
The chromosomal location of the active NORs has been analyzed by a silver impregnation procedure in theSteropleurus martorelli complex. A primary NOR, which is always present at the first meiotic prophase, has been found in each of the four described races. In addition to this, all races possess one or two secondary NORs which are less active than the former and can be occasionally shown. Usually only one of the two homologous chromosomes has been found to be involved with nucleolus organisation.These results are discussed in relation to hypotheses on the chromosome differentiation of this species complex. 相似文献
133.
134.
135.
136.
137.
Alicia Mimbrera Luis Rivas Faustino Mollinedo Emilio Muñoz Vicente Larraga 《Molecular and cellular biochemistry》1983,56(1):73-80
Summary The combined use of proteolytic digestion and lactoperoxidase catalyzed labelling with [125I] applied to membrane-bound or soluble pure F1-ATPase from Micrococcus lysodeikticus has allowed us to establish the topography of its , , and subunits within the protein molecule and with respect to the plane of the membrane.The subunit is most externally located to the membrane bilayer looking towards the cytoplasmic face, a position consistent with its proposed catalytic role. The and subunits lie in an intermediate layer between the subunits and the membrane, in which the subunit occupies a central position within the F1-ATPase molecule in contact with the subunit. The subunit appears to be tightly bound to the F0 component of the ATPase complex, probably buried in the membrane bilayer. A molecular arrangement of M. lysodeikticus ATPase is proposed that, taking into account the subunit stoichiometry 3 3 2 2 (MW 420 000), accommodates the role assigned to each subunit and most, if not all, the known properties of this bacterial energy-transducing protein. 相似文献
138.
G. M. Besser Lynne Parke C. R. W. Edwards Isabel A. Forsyth A. S. McNeilly 《BMJ (Clinical research ed.)》1972,3(5828):669-672
In five patients with inappropriate lactation and amenorrhoea or impotence brom-ergocryptine was found to suppress the lactation and to diminish the raised plasma prolactin levels. The responses to treatment suggest that there may be an inverse relationship between prolactin secretion and gonadotrophin secretion in man. 相似文献
139.
An evaluation of four methods for measuring cholesterol absorption by the intestine in man 总被引:11,自引:0,他引:11
Critical comparisons have been made in 12 patients of four methods for measuring cholesterol absorption from the intestine. Methods I-III depend on the use of labeled cholesterol (intravenously or continuous labeling orally) in conjunction with sterol balance measurements; Method IV can be carried out with only a single test dose containing labeled cholesterol plus labeled beta-sitosterol. In the latter technique absorption is calculated as the loss of cholesterol relative to beta-sitosterol during intestinal transit. Method III (isotopic steady-state method) proved to be undependable because of uncertainties in determining the existence of an isotopic steady state. However, Method IV gave good agreement with Methods I and II, and it appears to have certain practical as well as theoretical advantages. Although Method IV requires collections of stools for up to 8 days, it is nevertheless the most rapid and the simplest of all the methods for estimating absorption. It can also be used in certain situations, such as in fur-licking animals, when Methods I and II are inadequate. Therefore, this method would seem to be a valuable addition to other isotopic techniques for estimating cholesterol absorption in man. 相似文献
140.
Studies on the interaction of cholesterol absorption, synthesis, and excretion were carried out in eight patients using sterol balance techniques. Absorption of dietary cholesterol was found to increase with intake; up to 1 g of cholesterol was absorbed in patients fed as much as 3 g per day. In most patients, increased absorption of cholesterol evoked two compensatory mechanisms: (a) increased reexcretion of cholesterol (but not of bile acids), and (b) decrease in total body synthesis. However, the amount of suppression in synthesis was extremely variable from one patient to another; one patient had no decrease in synthesis despite a large increment in absorption of dietary cholesterol, and two patients showed a complete suppression of synthesis. In the majority of cases the accumulation of cholesterol in body pools was small because of adequate compensation by reexcretion plus reduced synthesis, but in a few patients large accumulations occurred on high cholesterol diets when absorption exceeded the compensatory mechanisms. These accumulations were not necessarily reflected in plasma cholesterol levels; these increased only slightly or not at all. 相似文献