全文获取类型
收费全文 | 343881篇 |
免费 | 28632篇 |
国内免费 | 268篇 |
出版年
2021年 | 3286篇 |
2019年 | 2949篇 |
2018年 | 5124篇 |
2017年 | 4846篇 |
2016年 | 6466篇 |
2015年 | 7655篇 |
2014年 | 8870篇 |
2013年 | 12105篇 |
2012年 | 13627篇 |
2011年 | 13700篇 |
2010年 | 9309篇 |
2009年 | 8029篇 |
2008年 | 11620篇 |
2007年 | 11611篇 |
2006年 | 11125篇 |
2005年 | 10134篇 |
2004年 | 10048篇 |
2003年 | 9479篇 |
2002年 | 9089篇 |
2001年 | 14459篇 |
2000年 | 14237篇 |
1999年 | 11010篇 |
1998年 | 3632篇 |
1997年 | 3449篇 |
1996年 | 3428篇 |
1995年 | 3143篇 |
1994年 | 3043篇 |
1992年 | 8327篇 |
1991年 | 8043篇 |
1990年 | 8065篇 |
1989年 | 7925篇 |
1988年 | 7240篇 |
1987年 | 6920篇 |
1986年 | 6194篇 |
1985年 | 6551篇 |
1984年 | 5199篇 |
1983年 | 4508篇 |
1982年 | 3228篇 |
1981年 | 2976篇 |
1979年 | 4851篇 |
1978年 | 3679篇 |
1977年 | 3443篇 |
1976年 | 3319篇 |
1975年 | 3907篇 |
1974年 | 4202篇 |
1973年 | 4188篇 |
1972年 | 3672篇 |
1971年 | 3382篇 |
1970年 | 3112篇 |
1969年 | 2954篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
S Furuto-Kato A Matsumoto N Kitamura S Nakanishi 《The Journal of biological chemistry》1985,260(22):12054-12059
Three types of cloned cDNA sequences for rat low molecular weight prekininogens were isolated and determined by molecular cloning and sequence analysis. The deduced amino acid sequences indicated that one, termed K-prekininogen, represents the counterpart of the known low molecular weight prekininogen present in other mammals, while the other two, called T-prekininogens, contain a novel T-kinin sequence which was recently identified from rat plasma. Although T- and K-prekininogens are highly homologous with each other, both of the T-prekininogens contain methionine, instead of arginine or lysine, as an amino acid preceding T-kinin and exhibit two consecutive amino acid deletions in the preceding region of T-kinin as compared with K-prekininogen. The former finding accounts for the previous observation of strong resistance of T-kininogens to cleavage with trypsin or kallikreins, while the latter finding has been explained by the structural analysis of genomic clones in which T-kinin-coding exon is contracted at its intron junction. A partial nucleotide sequence reported recently for the rat major acute phase protein (alpha 1-MAP) mRNA was found to be extremely related to the corresponding portion of the rat T-prekininogen mRNA. Furthermore, consistent with the previous report of the structural identity of major acute phase protein and alpha 1-cysteine proteinase inhibitor, kininogen closely resembles not only the former but also the latter in the amino acid compositions. The interrelationship among the triad of these proteins has been discussed. 相似文献
72.
D Laky S Constantinescu G Filipescu N M Constantinescu E Ratea F Halalau 《Morphologie et embryologie》1980,26(2):173-177
The first ten days' evolution of post-ischaemic lesions of the premonitory or angina pectoris syndrome type was experimentally studied by the challenge of a short-term (10 and 15 min) ischaemia, of an adaptation to ischaemia and an adaptation followed by prolonged ischaemia (20 and 35 min). Worthy of note was the persistence of reversible lesions after short-term ischaemia and adaptation, and the progressive evolution towards cytolysis and cicatrization of some pancicellular foci after adaptation followed by prolonged ischaemia. The role of mitochondrial lesions, of lysosomal hydrolases, the inefficiency of renewed circulation, as well as problems of diagnosis are discussed. 相似文献
73.
The review summarizes the authors’ and literature data on accumulation of DNA breaks in differentiating cells. Large 50-kb free DNA fragments were observed by several research teams in non-apoptotic insect, mammal, and plant cells. More intense DNA breakage was observed during maturation of spermatides, embryo development, and differentiation of myotubes, epidermal cells, lymphocytes, and neutrophils. In general, accumulation of DNA breaks in differentiating cells cannot be attributed to a decrease in the DNA repair efficiency. Poly(ADP)ribose synthesis often follows the DNA breakage in differentiating cells. We hypothesize that DNA fragmentation is an epigenetic tool for regulating the differentiation process. Scarce data on localization of the differentiation-associated DNA breaks indicate their preferable accumulation in specific DNA sequences including the nuclear matrix attachment sites. The same sites are degraded at early stages of apoptosis. Recent data on non-apoptotic function of caspases provide more evidence for possible existence of a DNA breakage mechanism in differentiating cells, resembling the initial stage of apoptosis. Excision of methylated cytosine and recombination are other possible explanations of the phenomenon. Elucidation of mechanisms of differentiation-induced DNA breaks appears to be a prospective research direction. 相似文献
74.
Páraic ó Cuív Rajesh Gupta Hareshwar P. Goswami Mark Morrison 《Applied and environmental microbiology》2013,79(19):6173-6175
Clostridium thermocellum encodes a cellulosomal, modular, and thermostable serine protease inhibitor (serpin), PinA. PinA stability but not inhibitory activity is affected by the Fn(III) and Doc(I) domains, and PinA is a broad inhibitor of subtilisin-like proteases and may play a key role in protecting the cellulosome from protease attack. 相似文献
75.
76.
77.
78.
The relations between the saccus lacrimalis and different portions of the musculus orbicularis oculi were studied in orbital regions of human fetuses sectioned into numbered series. No insertions of the pars lacrimalis or Horner's muscle on the saccus were found. These muscular fibres pass along the dorsal wall of the saccus and are separated from it by the reflex tendon of the ligamentum palpebrale mediale. The only muscular fibres that insert on the saccus are those that approach the anterior face of the saccus and the fornix. The fibres that insert on the anterior face proceed from the deep bundles of the pars preseptalis of the lower eyelids, and those that insert on the fornix derive from the deep bundles of the pars preseptalis of the upper eyelid. 相似文献
79.
The microvasculature of the skin of the hand of Japanese monkeys was examined by means of scanning electron microscopy of corrosion casts. The vasculature of all areas of the skin of the hand was examined and divided into three structures excluding the nail bed: (1) In the ball of the finger, the typical structure of the capillary loops was studied. Capillary loops were formed out of not just one capillary vessel, but two or three vessels. Each capillary vessel arose and divided into several branches at the papilla, and they became descending limbs. After the loop passed a hairpin turn, the descending limbs were 1.5 times larger than the ascending limbs in the intrapapillary portion, and they became extrapapillary venules. The descending limbs connected with the postcapillary venules in the postpapillary portion and with the horizontal network. The postcapillary venules fused with each other (1-5 loops) to form the primary and secondary venous arcades. (2) In the thenar eminence, the capillary loops were a little lower, and their grooves were wider than in the ball of the finger. The characteristic structure in this area was the interpapillar capillary network. (3) In the lateral side of the finger, the number of capillary loops formed by the arterial capillary network of the subepidermal layer was smaller. The capillary loops here had the lowest height and a simple structure. 相似文献
80.
N. Wada Y. Kanda M. Tokuriki K. Kanda 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》2000,186(7-8):771-779
We studied neuronal pathways from low-threshold muscle (group I, II) and cutaneous afferents (group A(alpha)beta) innervating the tail to motoneurons innervating trunk muscles (m. iliocostalis lumborum and m. obliquus externus abdominus) in 18 spinalized cats. Stimulation of group I muscle afferents produced excitatory postsynaptic potentials or excitatory postsynaptic potentials followed by inhibitory postsynaptic potentials in all motoneurons innervating the m. iliocostalis lumborum which showed effects (32%), and predominantly inhibitory postsynaptic potentials in motoneurons innervating the m. obliquus externus abdominus (47%). Stimulation of group I+II afferents produced significant increases of the incidence of motoneurons showing postsynaptic potentials (the notoneurons innervating the m. iliocostalis lumborum, 87%; the motoneurons innervating the m. obliquus externus abdominus, 82%). The effects of low threshold cutaneous afferents were bilateral, predominantly producing inhibitory postsynaptic potentials in motoneurons innervating both muscles. These results suggest that neuronal pathways from muscle afferents to back muscle motoneurons mainly increase the stiffness of the trunk to maintain its stability, while those to abdominal muscles help to extend the dorsal column by decreasing their activities. The results also indicate that neuronal pathways from cutaneous afferents to trunk motoneurons functionallY disconnect the tail from the trunk. 相似文献