全文获取类型
收费全文 | 4436篇 |
免费 | 362篇 |
国内免费 | 4篇 |
专业分类
4802篇 |
出版年
2022年 | 26篇 |
2021年 | 49篇 |
2020年 | 29篇 |
2019年 | 48篇 |
2018年 | 47篇 |
2017年 | 57篇 |
2016年 | 103篇 |
2015年 | 163篇 |
2014年 | 200篇 |
2013年 | 271篇 |
2012年 | 325篇 |
2011年 | 315篇 |
2010年 | 189篇 |
2009年 | 185篇 |
2008年 | 270篇 |
2007年 | 287篇 |
2006年 | 253篇 |
2005年 | 259篇 |
2004年 | 249篇 |
2003年 | 241篇 |
2002年 | 219篇 |
2001年 | 41篇 |
2000年 | 37篇 |
1999年 | 55篇 |
1998年 | 69篇 |
1997年 | 42篇 |
1996年 | 43篇 |
1995年 | 45篇 |
1994年 | 33篇 |
1993年 | 35篇 |
1992年 | 45篇 |
1991年 | 32篇 |
1990年 | 38篇 |
1989年 | 26篇 |
1988年 | 28篇 |
1987年 | 32篇 |
1986年 | 25篇 |
1985年 | 26篇 |
1984年 | 42篇 |
1983年 | 17篇 |
1982年 | 35篇 |
1981年 | 17篇 |
1980年 | 11篇 |
1979年 | 15篇 |
1978年 | 18篇 |
1977年 | 12篇 |
1976年 | 13篇 |
1975年 | 18篇 |
1974年 | 11篇 |
1969年 | 10篇 |
排序方式: 共有4802条查询结果,搜索用时 15 毫秒
51.
52.
A facile chemical synthesis of 1,2-dioleoyl and 1,2-dimyristoyl-sn-glycero-3-phospho-L-serine as well as the synthesis of several deuterated derivatives of phosphatidylserine (2 and 3 positions of serine and in the 3-glycerol position) are described. 360 MHz 1H NMR spectra of phosphatidylserine and the optical activity of various phosphatidylserine diastereomers were measured. 相似文献
53.
l-(+)-Bornesitol was detected in 23 of 33 genera of Gentianaceae investigated. The only subtribe without l-(+)-bornesitol (3 species tested) was Exacinae. None of the five genera of Menyanthaceae examined were found to contain l-(+)-bornesitol. 相似文献
54.
Joachim Pohlmann 《Phytochemistry》1975,14(7):1587-1589
The cucurbitacins in roots of Bryonia dioica and B. alba have been investigated. Both species contain the cucurbitacins E, B, I, D, J, K and L, the dihydrocucurbitacins E and B, and tetrahydrocucurbitacin I. The detection of certain cucurbitacin aglycones depends upon the date of harvest, the duration of storage and the methods used for extraction. 相似文献
55.
56.
Prof. Dr. Manfred Gersch Heiner Birkenbeil Joachim Ude 《Cell and tissue research》1975,160(3):389-397
The prothoracic glands of the last instar of Galleria mellonella undergo characteristic alterations of their cellular fine structure closely related to cellular activity. During progressive secretory activity of the gland cells there are extensive plasmalemmal infoldings and formation of a pronounced lacunar system. Mitochondria of the active cell phase are characterized by a specific increase in size and paler colour of the matrix. In contrast to the alterations, nuclei, ER and Golgi cisterns do not undergo any submicroscopic changes during the different phases of cellular activity. The relationship between the substructural phenomena and the specific phases of cellular activity are discussed. 相似文献
57.
Ulrike Winter Nicolas Stankovic‐Valentin Petra Haas Kay Hofmann Henning Urlaub Huib Ovaa Joachim Wittbrodt Erik Meulmeester Frauke Melchior 《EMBO reports》2012,13(10):930-938
Isopeptidases are essential regulators of protein ubiquitination and sumoylation. However, only two families of SUMO isopeptidases are at present known. Here, we report an activity‐based search with the suicide inhibitor haemagglutinin (HA)‐SUMO‐vinylmethylester that led to the identification of a surprising new SUMO protease, ubiquitin‐specific protease‐like 1 (USPL1). Indeed, USPL1 neither binds nor cleaves ubiquitin, but is a potent SUMO isopeptidase both in vitro and in cells. C13orf22l—an essential but distant zebrafish homologue of USPL1—also acts on SUMO, indicating functional conservation. We have identified invariant USPL1 residues required for SUMO binding and cleavage. USPL1 is a low‐abundance protein that colocalizes with coilin in Cajal bodies. Its depletion does not affect global sumoylation, but causes striking coilin mislocalization and impairs cell proliferation, functions that are not dependent on USPL1 catalytic activity. Thus, USPL1 represents a third type of SUMO protease, with essential functions in Cajal body biology. 相似文献
58.
Nicola Gasparini Michael Salvador Sebastian Strohm Thomas Heumueller Ievgen Levchuk Andrew Wadsworth James H. Bannock John C. de Mello Hans‐Joachim Egelhaaf Derya Baran Iain McCulloch Christoph J. Brabec 《Liver Transplantation》2017,7(19)
Organic solar cells that are free of burn‐in, the commonly observed rapid performance loss under light, are presented. The solar cells are based on poly(3‐hexylthiophene) (P3HT) with varying molecular weights and a nonfullerene acceptor (rhodanine‐benzothiadiazole‐coupled indacenodithiophene, IDTBR) and are fabricated in air. P3HT:IDTBR solar cells light‐soaked over the course of 2000 h lose about 5% of power conversion efficiency (PCE), in stark contrast to [6,6]‐Phenyl C61 butyric acid methyl ester (PCBM)‐based solar cells whose PCE shows a burn‐in that extends over several hundreds of hours and levels off at a loss of ≈34%. Replacing PCBM with IDTBR prevents short‐circuit current losses due to fullerene dimerization and inhibits disorder‐induced open‐circuit voltage losses, indicating a very robust device operation that is insensitive to defect states. Small losses in fill factor over time are proposed to originate from polymer or interface defects. Finally, the combination of enhanced efficiency and stability in P3HT:IDTBR increases the lifetime energy yield by more than a factor of 10 when compared with the same type of devices using a fullerene‐based acceptor instead. 相似文献
59.
Dennis A. Nowak Stefan Glasauer Ludger Meyer Norbert Mai Joachim Hermsdörfer 《Somatosensory & motor research》2013,30(1):49-60
Grip force adjustments to changes of object loading induced by external changes of the direction of gravity during discrete arm movements with a grasped object were analyzed during normal and anesthetized finger sensibility. Two subjects were seated upright in a rotatable chair and rotated backwards into a horizontal position during discrete movements with a hand-held instrumented object. The movement direction varied from vertical to horizontal inducing corresponding changes in the direction of gravity, but the orientation of the movement in relation to the body remained unaffected. During discrete vertical movements a maximum of load force occurs early in upward and late in downward movements; during horizontal movements two load force peaks result from both acceleratory and deceleratory phases of the movement. During performance with normal finger sensibility grip force was modulated in parallel with fluctuations of load force during vertical and horizontal movements. The grip force profile adopted to the varying load force profile during the transition from the vertical to the horizontal position. The maximum grip force occurred at the same time of maximum load force irrespective of the movement plane. During both subjects' first experience of digital anesthesia the object slipped from the grasp during rotation to the horizontal plane. During the following trials with anesthetized fingers subjects substantially increased their grip forces, resulting in elevated force ratios between maximum grip and load force. However, grip force was still modulated with the movement-induced load fluctuations and maximum grip force coincided with maximum load force during vertical and horizontal movements. This implies that the elevated force ratio between maximum grip and load force does not alter the feedforward system of grip force control. Cutaneous afferent information from the grasping digits seems to be important for the economic scaling of the grip force magnitude according to the actual loading conditions and for reactive grip force adjustments in response to load perturbations. However, it plays a subordinate role for the precise anticipatory temporal coupling between grip and load forces during voluntary object manipulation. 相似文献
60.
Haberer G Young S Bharti AK Gundlach H Raymond C Fuks G Butler E Wing RA Rounsley S Birren B Nusbaum C Mayer KF Messing J 《Plant physiology》2005,139(4):1612-1624
Maize (Zea mays or corn) plays many varied and important roles in society. It is not only an important experimental model plant, but also a major livestock feed crop and a significant source of industrial products such as sweeteners and ethanol. In this study we report the systematic analysis of contiguous sequences of the maize genome. We selected 100 random regions averaging 144 kb in size, representing about 0.6% of the genome, and generated a high-quality dataset for sequence analysis. This sampling contains 330 annotated genes, 91% of which are supported by expressed sequence tag data from maize and other cereal species. Genes averaged 4 kb in size with five exons, although the largest was over 59 kb with 31 exons. Gene density varied over a wide range from 0.5 to 10.7 genes per 100 kb and genes did not appear to cluster significantly. The total repetitive element content we observed (66%) was slightly higher than previous whole-genome estimates (58%-63%) and consisted almost exclusively of retroelements. The vast majority of genes can be aligned to at least one sequence read derived from gene-enrichment procedures, but only about 30% are fully covered. Our results indicate that much of the increase in genome size of maize relative to rice (Oryza sativa) and Arabidopsis (Arabidopsis thaliana) is attributable to an increase in number of both repetitive elements and genes. 相似文献