全文获取类型
收费全文 | 9993篇 |
免费 | 808篇 |
国内免费 | 3篇 |
出版年
2022年 | 56篇 |
2021年 | 112篇 |
2020年 | 104篇 |
2019年 | 95篇 |
2018年 | 101篇 |
2017年 | 121篇 |
2016年 | 197篇 |
2015年 | 331篇 |
2014年 | 376篇 |
2013年 | 504篇 |
2012年 | 576篇 |
2011年 | 518篇 |
2010年 | 381篇 |
2009年 | 332篇 |
2008年 | 511篇 |
2007年 | 550篇 |
2006年 | 536篇 |
2005年 | 484篇 |
2004年 | 522篇 |
2003年 | 492篇 |
2002年 | 508篇 |
2001年 | 135篇 |
2000年 | 125篇 |
1999年 | 161篇 |
1998年 | 149篇 |
1997年 | 123篇 |
1996年 | 111篇 |
1995年 | 140篇 |
1994年 | 127篇 |
1993年 | 128篇 |
1992年 | 121篇 |
1991年 | 139篇 |
1990年 | 104篇 |
1989年 | 95篇 |
1988年 | 82篇 |
1987年 | 97篇 |
1986年 | 82篇 |
1985年 | 110篇 |
1984年 | 114篇 |
1983年 | 81篇 |
1982年 | 103篇 |
1981年 | 94篇 |
1980年 | 78篇 |
1979年 | 67篇 |
1978年 | 61篇 |
1977年 | 57篇 |
1975年 | 56篇 |
1974年 | 51篇 |
1973年 | 62篇 |
1972年 | 53篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Summary The pattern of intercellular connections between germ line cells has been studied in follicles of the mutantdicephalic (dic), which possess nurse cell clusters at both poles. Staining of follicles with a fluorescent rhodamine conjugate of phalloidin reveals ring canals and cell membranes and thus allows us to reconstruct the spatial organization of the follicle. Each germ line cell can be identified by the pattern of cell-cell connections which reflect the mitotic history of individual cells in the 16-cell cluster. The results indicate that in both wild-type anddicephalic cystocyte clusters one of the two cells with four ring canals normally becomes the pro-oocyte. However, in some follicles (dicephalic and wild-type) oocytes were found with fewer or more than four ring canals. Indic follicles, one or several nurse cells may become disconnected from the other cells during oocyte growth at stage 9–10. Such disconnected cells cannot later on empty their cytoplasm into the oocyte. This, in turn, might be of consequence for the determination of axial polarity of the embryo. 相似文献
2.
3.
Summary In the initial phase of the geotropical reaction of the Chara rhizoid the growth difference postulated by Sievers (1967c) between the physically upper, slightly subapical flank and the lower one is demonstrated. In horizontal exposure the growth of the extreme cell apex is continued, while the growth of the lower flank is inhibited and that of the upper one is promoted. In the end phase the cell apex shows a damped oscillation until it finally reaches the vertical growth direction. The statoliths follow the oscillating growth of the cell tip from one flank to the opposite one until they are statistically equally redistributed in their normal position.—In vertical exposure under reduced turgor pressure the statoliths fall down into the extreme cell apex, where they inhibit the growth of this part of the cell wall, while the subapical wall grows transversally.—It is concluded that the statoliths inhibit the growth of the cell wall area which they cover.—The physical phase of the reaction chain, the susception, is the gravity-induced downward displacement of the statoliths. The physiological phase starts with the diversion of the acropetal transport of the Golgi vesicles to the upper part of the cell, which is caused by the block of statoliths (perception). The greater rate of vesicle incorporation into the upper flank in comparison to the lower one causes the subapical growth difference which results in the curvature (reaction).—In the case of the Chara rhizoid Golgi- and statolith-apparatus function as a self-regulating cellular system.
Herrn Prof. Dr. Dr. h. c. Kurt Mothes zum 70. Geburtstag. 相似文献
Herrn Prof. Dr. Dr. h. c. Kurt Mothes zum 70. Geburtstag. 相似文献
4.
5.
Surface sediment samples taken by ? corer from 45 stations on the Norwegian continental margin and in the Norway Basin have been investigated for their benthic foraminiferal content. Unlike previous studies, the living benthic foraminiferal fauna was differentiated from empty tests comprising the foraminiferal death assemblage. Factor analysis of both the living and dead faunal data reveals six living species assemblages and five corresponding dead assemblages. The additional living assemblage is characterized by the arenaceous speciesCribrostomoides subglobosum that dominates between 1400 and 2000 m water depth, but is rare in the dead faunal data.Trifarina angulosa and, to a lesser extent,Cibicides lobatulus characterize the shallowest foraminiferal assemblage from 200 to 600 m water depth, where it is associated with strong bottom currents and warm, saline Atlantic water of the North Atlantic Drift. On the slope between 600 and 1200 m water depth, theMelonis zaandami Species Assemblage dominates, particularly in areas characterized today by rapid sedimentation of terrigeneous material. Between 1000 and 1400 m depth, where the slope is covered by fine grained, organic-rich, terrigeneous mud, the living foraminiferal assemblage is characterized byCassidulina teretis andPullenia bulloides. Below 1400 m, three foraminiferal assemblages are found:C. subglobosum is found from 1400 to 2000 m,Cibicidoides wuellerstorfi andEpistominella exigua predominantly live from 2000 to 3000 m water depth, and below 3000 m,Oridorsalis umbonatus andTriloculina frigida dominate the fauna.All of theElphidium excavatum tests found in this study and theCassidulina reniforme tests found above 500 m water depth were found to be reworked.Analysis of the sediment grain-size distribution and the organic carbon content in surface samples from the deepest stations suggest that the abundance ofC. wuellerstorfi andE. exigua is positively correlated to relatively coarse (caused by planktic foraminifera) and organic-rich sediments, whereas high frequencies ofO. umbonatus andT. frigida coincide with low organic carbon content. We suggest thatC. wuellerstorfi is adapted to deep-sea environments with relatively high food supply, tolerating relatively low interstitial water oxygen content, whereasO. umbonatus may tolerate lower food supply prefering well-oxygenated interstitial waters. 相似文献
6.
7.
Se-Chan Kim Alexander Ghanem Heidi Stapel Klaus Tiemann Pascal Knuefermann Andreas Hoeft Rainer Meyer Christian Grohé Anne A Knowlton Georg Baumgarten 《BMC physiology》2007,7(1):5
Backgound
It has been reported that Toll-like receptor 4 (TLR4) deficiency reduces infarct size after myocardial ischemia/reperfusion (MI/R). However, measurement of MI/R injury was limited and did not include cardiac function. In a chronic closed-chest model we assessed whether cardiac function is preserved in TLR4-deficient mice (C3H/HeJ) following MI/R, and whether myocardial and systemic cytokine expression differed compared to wild type (WT). 相似文献8.
9.
10.
Siegfried Huneck Klaus Schreiber Hans Dieter Grimmecke 《Journal of Plant Growth Regulation》1984,3(1-3):75-84
Seventy-two Schiffs bases, 44 corresponding secondary amines, and 12 N-acetylated compounds were tested on their growth activity. Eighty-one compounds were active as growth inhibitors in at least one of three bioassays. 相似文献