全文获取类型
收费全文 | 1781篇 |
免费 | 104篇 |
国内免费 | 4篇 |
出版年
2023年 | 13篇 |
2022年 | 20篇 |
2021年 | 77篇 |
2020年 | 39篇 |
2019年 | 46篇 |
2018年 | 71篇 |
2017年 | 57篇 |
2016年 | 73篇 |
2015年 | 100篇 |
2014年 | 118篇 |
2013年 | 132篇 |
2012年 | 171篇 |
2011年 | 171篇 |
2010年 | 86篇 |
2009年 | 65篇 |
2008年 | 100篇 |
2007年 | 68篇 |
2006年 | 70篇 |
2005年 | 68篇 |
2004年 | 56篇 |
2003年 | 44篇 |
2002年 | 35篇 |
2001年 | 16篇 |
2000年 | 19篇 |
1999年 | 15篇 |
1998年 | 8篇 |
1997年 | 7篇 |
1996年 | 5篇 |
1995年 | 6篇 |
1994年 | 6篇 |
1993年 | 10篇 |
1992年 | 12篇 |
1991年 | 8篇 |
1990年 | 12篇 |
1989年 | 6篇 |
1987年 | 4篇 |
1986年 | 7篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1980年 | 6篇 |
1978年 | 3篇 |
1977年 | 6篇 |
1975年 | 5篇 |
1974年 | 3篇 |
1973年 | 4篇 |
1972年 | 5篇 |
1967年 | 3篇 |
排序方式: 共有1889条查询结果,搜索用时 171 毫秒
21.
Copper metabolism in a teleost, the plaice, Pleuronectes platessa (L.) from a natural environment has been studied. Distribution in the various tissues of the metal and of five key copper-dependent enzymes: ceruloplasmin EC 1.16.3.1; Superoxide dismutase EC 1.15.11; tryptophan oxygenase EC 1.13.1.12; cytochrome oxidase EC 1.9.3.1 and monoamine oxidase EC 1.4.3.4 have been determined. The copper distribution was found to be similar to that in mammals with the greatest concentrations in the brain and heart. Distribution of the copper enzymes is also similar to that found in mammals. A preliminary characterization of the copper enzymes showed that plaice cytochrome oxidase has a pH maximum 2 pH units more alkaline than the mammalian enzyme and that plaice tryptophan oxygenase is more sensitive to heat denaturation than the mammalian enzyme. The present data form a base-line against which studies on factors affecting the copper metabolism in a teleost can be assessed. 相似文献
22.
The role of chlorinated primary effluents in viral pollution of the Ottawa River (Ontario) was assessed by examining 282 field samples of wastewaters from two different sewage treatment plants over a 2-year period. The talc-Celite technique was used for sample concentration, and BS-C-1 cells were employed for virus detection. Viruses were detected in 80% (75/94) of raw sewage, 72% (68/94) of primary effluent, and 56% (53/94) of chlorinated effluent samples. Both raw sewage and primary effluent samples contained about 100 viral infective units (VIU) per 100 ml. Chlorination produced a 10- to 50-fold reduction in VIU and gave nearly 2.7 VIU/100 ml of chlorinated primary effluent. With a combined daily chlorinated primary effluent output of approximately 3.7 × 108 liters, these two plants were discharging 1.0 × 1010 VIU per day. Because the river has a mean annual flow of 8.0 × 1010 liters per day, these two sources alone produced a virus loading of 1.0 VIU/8 liters of the river water. This river also receives at least 9.0 × 107 liters of raw sewage per day and undetermined but substantial amounts of storm waters and agricultural wastes. It is used for recreation and acts as a source of potable water for some 6.0 × 105 people. In view of the potential of water for disease transmission, discharge of such wastes into the water environment needs to be minimized. 相似文献
23.
24.
25.
26.
Syed Siraj-ul-Islam Chintala V.N. Rao Atindra N. Chakraborty S. Ghosh Dastidar 《Carbohydrate research》1982,110(1):69-75
The lipopolysaccharide isolated from the cells of Shigella boydii type 8 bacteria gave precipitin bands against homologous antisera on Ouchterlony plates, whereas the carbohydrate-containing fractions obtained from it did not. One of the fractions was obtained in major proportion and contained 23.5% of sugars. A structure was assigned to the carbohydrate chain in this material by using the results of methylation, periodate oxidation, and deamination studies. 相似文献
27.
In this paper, a fractional complex transform (FCT) is used to convert the given fractional partial differential equations (FPDEs) into corresponding partial differential equations (PDEs) and subsequently Reduced Differential Transform Method (RDTM) is applied on the transformed system of linear and nonlinear time-fractional PDEs. The results so obtained are re-stated by making use of inverse transformation which yields it in terms of original variables. It is observed that the proposed algorithm is highly efficient and appropriate for fractional PDEs and hence can be extended to other complex problems of diversified nonlinear nature. 相似文献
28.
Mohyeddin Mandana Bonab Kamran Alimoghaddam Fatemeh Talebian Syed Hamid Ghaffari Ardeshir Ghavamzadeh Behrouz Nikbin 《BMC cell biology》2006,7(1):14-7
Background
A hot new topic in medical treatment is the use of mesenchymal stem cells (MSC) in therapy. The low frequency of this subpopulation of stem cells in bone marrow (BM) necessitates their in vitro expansion prior to clinical use. We evaluated the effect of long term culture on the senescence of these cells. 相似文献29.
Syed Mohsin Waheed Arnab Ghosh Ritu Chakravarti Ashis Biswas Mohammad Mahfuzul Haque Koustubh Panda Dennis J. Stuehr 《Free radical biology & medicine》2010,48(11):1548-1558
Although the insertion of heme into proteins enables their function in bioenergetics, metabolism, and signaling, the mechanisms and regulation of this process are not fully understood. We developed a means to study cellular heme insertion into apo-protein targets over a 3-h period and then investigated how nitric oxide (NO) released from a chemical donor (NOC-18) might influence heme (protoporphyrin IX) insertion into seven targets that present a range of protein structures, heme ligation states, and functions (three NO synthases, two cytochrome P450's, catalase, and hemoglobin). NO blocked cellular heme insertion into all seven apo-protein targets. The inhibition occurred at relatively low (nM/min) fluxes of NO, was reversible, and did not involve changes in intracellular heme levels, activation of guanylate cyclase, or inhibition of mitochondrial ATP production. These aspects and the range of protein targets suggest that NO can act as a global inhibitor of heme insertion, possibly by inhibiting a common step in the process. 相似文献