全文获取类型
收费全文 | 282331篇 |
免费 | 24744篇 |
国内免费 | 264篇 |
专业分类
307339篇 |
出版年
2018年 | 3732篇 |
2017年 | 3524篇 |
2016年 | 4758篇 |
2015年 | 5431篇 |
2014年 | 6354篇 |
2013年 | 8937篇 |
2012年 | 9961篇 |
2011年 | 10421篇 |
2010年 | 6975篇 |
2009年 | 5982篇 |
2008年 | 8774篇 |
2007年 | 8951篇 |
2006年 | 8624篇 |
2005年 | 7955篇 |
2004年 | 7862篇 |
2003年 | 7539篇 |
2002年 | 7309篇 |
2001年 | 12905篇 |
2000年 | 12828篇 |
1999年 | 9834篇 |
1998年 | 2954篇 |
1997年 | 2931篇 |
1996年 | 2892篇 |
1995年 | 2680篇 |
1994年 | 2575篇 |
1993年 | 2449篇 |
1992年 | 7603篇 |
1991年 | 7341篇 |
1990年 | 7387篇 |
1989年 | 7182篇 |
1988年 | 6650篇 |
1987年 | 6300篇 |
1986年 | 5625篇 |
1985年 | 5930篇 |
1984年 | 4668篇 |
1983年 | 4051篇 |
1982年 | 2817篇 |
1981年 | 2618篇 |
1980年 | 2427篇 |
1979年 | 4343篇 |
1978年 | 3268篇 |
1977年 | 3009篇 |
1976年 | 2944篇 |
1975年 | 3403篇 |
1974年 | 3655篇 |
1973年 | 3680篇 |
1972年 | 3217篇 |
1971年 | 2990篇 |
1970年 | 2688篇 |
1969年 | 2453篇 |
排序方式: 共有10000条查询结果,搜索用时 7 毫秒
961.
S. N. Perova 《Inland Water Biology》2008,1(4):371-379
The macrozoobenthos taxonomic composition in small karst lakes of Vladimir oblast is studied for the first time. In the structure
of bottom communities, 149 taxa one rank below the genus have been found. Chironomid larvae and other amphibiotic animals,
as well as oligochaetes, prevail. Most of them are species widely distributed in the surface waters of European Russia. The
highest macrozoobenthos species diversity was recorded in neutral lakes, and the lowest diversity was in lakes with weakly
acidic waters. 相似文献
962.
Yu. S. Ravkin S. M. Tsybulin S. G. Livanov K. V. Toropov V. N. Kuranova V. P. Starikov S. V. Chesnokova 《Contemporary Problems of Ecology》2008,1(5):568-573
For the entire territory of West Siberia, including its plain and mountainous parts, two maps were constructed for populations of amphibians together with reptiles, and of birds. Communities of these classes of vertebrates differ from one another in their spatial differentiation. The differences are demonstrated for the plain and mountainous territories considered jointly and separately. 相似文献
963.
964.
965.
966.
967.
N A Grekova 《Zhurnal mikrobiologii, epidemiologii, i immunobiologii》1978,(8):109-112
Lysozyme content was determined in the subcutaneous cellular tissue of guinea pigs and albino rats differing by species resistance to brucella infection. Experiments were conducted on intact animals and those inoculated subcutaneously with live Br. abortus 19-BA vaccine. Connective tissue was taken from the site of the vaccine administration and from the contralateral side (control). Observations showed connective tissue of the animals highly sensitive to brucella infection to be exceedingly poor in this enzyme; as to connective tissue of albino rats with low sensitivity--it contained high amount of this enzyme. Lysozyme content increased considerably in the animals belonging to both species in the inflammatory focus developing at the site of the vaccine inoculation. 相似文献
968.
The intrinsic fluorescence of the enzyme rhodanese is quenched by as much as 30% when sulfur is transferred to the free enzyme form, E, giving the sulfur-substituted enzyme, ES. This fluorescence change (lambda ex = 295 nm and lambda em = 335 nm) has been used to quantitate the E and ES forms which are isolatable, obligatory intermediates in rhodanese catalysis. Fluorescence titration was performed using cyanide to irreversibly remove sulfur from ES. The results show a stoichiometry corresponding to 1 bound sulfur/molecule of the ES form of rhodanese (Mr = 33,000). The fluorescence changes were used to measure the concentrations of E and ES when these were in reversible equilibria induced by interactions with the substrates S2O3(2-) and SO3(2-). These results were compared with an equilibrium constant derived from published kinetic studies for the reaction (formula; see text) The very close agreement between the physical and kinetic methods indicate that there are no significant concentrations of intermediates other than E and ES. Overall, the results are compatible with the formation of a persulfide intermediate in rhodanese catalysis and are consistent with conclusions from x-ray crystallography and absorption spectroscopy. In addition, these procedures offer a facile method to measure equilibria between catalytic intermediates in the rhodanese reaction using functionally relevant concentrations. 相似文献
969.
970.
Several products derived from processed maca hypocotyls (Lepidium peruvianum Chacón, previously known asL. meyenii Walp.) were surveyed for glucosinolate content and quantified by HPLC analysis. These included pills, capsules, flour, liquor, tonic and mayonnaise. Different plant organs such as fresh hypocotyls and leaves, seeds, dry hypocotyls, and sprouts were also included in the survey. The most abundant glucosinolates detected in fresh and dry hypocotyls and leaves were the aromatic glucosinolates, benzylglucosinolate (glucotropaeolin) and p-methoxybenzylglucosinolate. Maca seeds and sprouts differed in profile from hypocotyls and leaves due to the modification of benzylglucosinolate. No glucosinolates were detected in liquor and tonic, while mayonnaise had only trace amounts of those glucosinolates. It had instead allylglucosinolate (sinigrin), which is an aliphatic glucosinolate. The pills, capsules and flour had the same glucosinolates as those observed in hypocotyls, but in variable amounts. The richest sources of glucosinolates were seeds, fresh hypocotyls and sprouts, in that order. 相似文献