全文获取类型
收费全文 | 42055篇 |
免费 | 4402篇 |
国内免费 | 11篇 |
出版年
2022年 | 348篇 |
2021年 | 698篇 |
2020年 | 496篇 |
2019年 | 582篇 |
2018年 | 710篇 |
2017年 | 637篇 |
2016年 | 1060篇 |
2015年 | 1766篇 |
2014年 | 1926篇 |
2013年 | 2395篇 |
2012年 | 2937篇 |
2011年 | 2872篇 |
2010年 | 1895篇 |
2009年 | 1653篇 |
2008年 | 2309篇 |
2007年 | 2306篇 |
2006年 | 2194篇 |
2005年 | 1972篇 |
2004年 | 1942篇 |
2003年 | 1739篇 |
2002年 | 1708篇 |
2001年 | 708篇 |
2000年 | 683篇 |
1999年 | 674篇 |
1998年 | 452篇 |
1997年 | 383篇 |
1996年 | 362篇 |
1995年 | 374篇 |
1994年 | 331篇 |
1993年 | 339篇 |
1992年 | 469篇 |
1991年 | 412篇 |
1990年 | 395篇 |
1989年 | 419篇 |
1988年 | 406篇 |
1987年 | 390篇 |
1986年 | 323篇 |
1985年 | 342篇 |
1984年 | 360篇 |
1983年 | 305篇 |
1982年 | 294篇 |
1981年 | 258篇 |
1980年 | 242篇 |
1979年 | 260篇 |
1978年 | 218篇 |
1977年 | 216篇 |
1976年 | 214篇 |
1975年 | 248篇 |
1974年 | 201篇 |
1973年 | 196篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
931.
Josette Martin-Tanguy Ferdinand Cabanne Etienne Perdrizet Claude Martin 《Phytochemistry》1978,17(11):1927-1928
Hydroxycinnamic acid amides have been identified as the main phenolic constituents in the reproductive organs of a range of flowering plants. 相似文献
932.
Sabine Voigt Salah El Kousy Nicola Schwelle Lutz Nover Martin Luckner 《Phytochemistry》1978,17(10):1705-1709
In the hyphae of Penicillium cyclopium the in vitro measurable activities of 3 enzymes of alkaloid biosynthesis are induced endogenously during 相似文献
933.
Uptake, transport and metabolism of cytokinin in the protonemaof Funaria hygrometrica were studied using labelled kinetin(6-furfurylamino [8-14C]-purine). All cells of the protonema,chloronema and caulonema, were able to take up kinetin, whichwas carried in the symplastic transport system from cell tocell. Radioactivity was especially accumulated in growing cellsof the protonema. Kinetin was metabolized immediately afteruptake. While only very little kinetin (less than 1%) remainedas free kinetin and one part was immobilized in chromatographicseparation [e.g. attached to proteins and incorporated intonucleic acids (17)], most of the remaining kinetin was metabolizedto adenine derivatives. Exogenously supplied adenosine changedthe metabolism of kinetin. In the caulonema, adenosine reducedthe turnover of kinetin to other adenine derivatives and enhancedthe content of labelling in the start fraction. Thus adenosinecan stimulate cytokinin-dependent bud formation in moss protonema. (Received November 24, 1977; ) 相似文献
934.
Soluble proteins extracted with Tris-buffer pH 8.8 from different mosses are analysed by microgelelectrophoretic method for comparison to the specific proteins present only in the caulonema of Funaria hygrometrica. The protein patterns are also compared with those of liverwort, fern gametophytes and sporophytes and tobacco. It is observed that the caulonema specific proteins are only present in the caulonema of these mosses and are absent in other plants.Abbreviations CSP
caulonema specific proteins 相似文献
935.
Henry R. Black Morton G. Glickman Martin Schiff Jr. Erik G. Pingoud 《The Yale journal of biology and medicine》1978,51(6):635-654
Renovascular hypertension can result from renal artery lesions involving the main renal artery, or its branches. It is generally felt that the elevation of blood pressure results from excessive systemic vasoconstriction secondary to enhanced renin secretion by one or part of one kidney. Renin secretion is enhanced because of constriction of the renal artery and resultant intrarenal ischemia. Clinically patients cannot be distinguished from those with essential hypertension and diagnosis must be made with arteriography although urography and isotope renography may suggest the diagnosis. Surgical cure can be predicted if differential renal vein renin ratios lateralize but a non-lateralizing study does not necessarily mean that surgery will fail. In properly selected patients, surgical results are excellent. 相似文献
936.
Martin A. Shearn 《The Western journal of medicine》1978,129(4):358-363
Important diagnostic clues may be provided by changes in the nails. Because nail findings are easily observable and yield valuable information, attention to these features is often rewarding. Some of the nail changes that may be observed in systemic disorders are reviewed. 相似文献
937.
Martin Dambach Leonhard Lichtenstein 《Ethology : formerly Zeitschrift fur Tierpsychologie》1978,46(1):14-29
In the East African cricket Phaeophilacris spectrum a few ♀♀ form a social group which is joined by a ♂ who defends the group against other ♂♂. There is a special courtship and aggressive behaviour with several action sequences. ♂♂ perform two types of non-stridulatory wing flicking. 相似文献
938.
939.
940.
Retinal bipolar cells constitute the output stage of the outer layer of the retina. There are several constraints on the ability of the bipolar cell array to respond to the different spatial frequency components of the visual image, including (i) electrical coupling in the dendritic tree receiving receptor input; (iii) the "lateral inhibition" mediated by horizontal cells. Using simple mathematical models, we derive analytical expressions for the spatial frequency response of the bipolar cell array for the case in which horizontal cells are presynaptic to bipolar cells (feedforward model) and also for the case in which horizontal cells are presynaptic to receptors (feedback model). The results illustrate the importance of the three factors mentioned in determining the bipolar cells' properties. The optimal spatial frequency for stimulating the bipolar cell array, and the range of spatial frequencies transmitted onward to the inner plexiform layer, are thus related to the anatomical and electrical properties of the cells in the outer plexiform layer. 相似文献