全文获取类型
收费全文 | 25426篇 |
免费 | 2438篇 |
国内免费 | 633篇 |
出版年
2023年 | 130篇 |
2022年 | 311篇 |
2021年 | 573篇 |
2020年 | 405篇 |
2019年 | 516篇 |
2018年 | 641篇 |
2017年 | 495篇 |
2016年 | 809篇 |
2015年 | 1257篇 |
2014年 | 1439篇 |
2013年 | 1630篇 |
2012年 | 2010篇 |
2011年 | 1896篇 |
2010年 | 1271篇 |
2009年 | 1020篇 |
2008年 | 1404篇 |
2007年 | 1336篇 |
2006年 | 1248篇 |
2005年 | 1109篇 |
2004年 | 1019篇 |
2003年 | 967篇 |
2002年 | 814篇 |
2001年 | 651篇 |
2000年 | 571篇 |
1999年 | 511篇 |
1998年 | 261篇 |
1997年 | 237篇 |
1996年 | 210篇 |
1995年 | 189篇 |
1994年 | 173篇 |
1993年 | 132篇 |
1992年 | 278篇 |
1991年 | 269篇 |
1990年 | 232篇 |
1989年 | 237篇 |
1988年 | 215篇 |
1987年 | 168篇 |
1986年 | 161篇 |
1985年 | 181篇 |
1984年 | 137篇 |
1983年 | 110篇 |
1982年 | 102篇 |
1981年 | 111篇 |
1979年 | 115篇 |
1978年 | 99篇 |
1977年 | 75篇 |
1976年 | 72篇 |
1975年 | 92篇 |
1974年 | 94篇 |
1973年 | 87篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
112.
Triterpene glycosides from Schefflera octophylla. 总被引:1,自引:0,他引:1
In addition to 3-epi-betulinic acid, three triterpene glycosides were isolated from leaves of Schefflera octophylla. The structures of the glycosides have been determined as 28-O-[alpha-L-rhamnopyranosyl(1----4)-O-beta-D-glucopyranosyl(1----6)-be ta-D- glucopyranosides of 3 alpha-hydroxy-lup-20(29)-ene-23,28-dioic acid, 3 alpha,11 alpha- dihydroxy-lup20(29)-ene-23,28-dioic acid and 3-epi-betulinic acid by spectroscopic data and chemical transformations. The last two compounds were found for the first time in the plant kingdom. 相似文献
113.
S H Chen Y L Chang W P Ho F C Wei M S Noordhoff 《Plastic and reconstructive surgery》1991,87(2):346-353
A successful simultaneous bilateral forearm revascularization was performed on a 17-year-old boy. Functional recovery of both forearms was evaluated 42 months after injury. The patient can use both hands for the activities of daily living. So far, he has been employed and has no significant psychological problems. Temporary intraluminal silicone shunts are extremely helpful for reducing ischemic damage to the injured limb. The sufficient skeletal shortening of the upper limb replantation is crucially important. The wounds must be managed by aggressive and repeated debridement. Accurate primary nerve repair is essential, and the early postoperative rehabilitation is also important to achieve a satisfactory functional return. The functional replanted or revascularized upper extremity is superior to an amputation or prosthesis, especially in the cases of bilateral upper extremity amputation or devascularization. 相似文献
114.
115.
116.
D. -L. Wei S. -C. Chang Y. -H. Wei Y. -W. Lin C. -L. Chuang S. -C. Jong 《World journal of microbiology & biotechnology》1992,8(2):141-146
Eighteen strains of xylariaceous fungi have been screened for higher activities of cellulolytic enzymes,Trichoderma reesei QM 9414 was also examined for comparison. Strains ofXylaria anisopleura andX. regalis had higher endocellulase (CMCase) and exocellulase (Avicelase) activities after 2 weeks' incubation.Hypoxylon stygium produced the highest activity of -glucosidase 3 days after inoculation. The optimum pH for these cellulolytic enzymes was approx. 5.0 and the optimum temperatures ranged from 37 to 50°C. A mixed culture process usingT. reesei QM 9414 andH. stygium was developed to obtain enhanced synthesis of cellulase. -Glucosidase activities in the mixed culture increased within 48h whenH. stygium was introduced after 24h. 相似文献
117.
M P Czech B M Clancy A Pessino C W Woon S A Harrison 《Trends in biochemical sciences》1992,17(5):197-201
Facilitated sugar entry into mammalian cells is catalysed by multiple isoforms of the glucose transporter and regulated by hormonal stimuli, nutritional status and oncogenesis. A large reserve of latent glucose transport capacity must be maintained by muscle and adipose cells that are sensitive to insulin, the primary activator of sugar uptake after feeding. Intracellular sequestration of sugar transporters accounts for a large part of this latent capacity, but new findings suggest that there is also reversible suppression of intrinsic catalytic activity of those glucose transporters residing at the cell surface. The mechanism of this suppression appears to be occlusion or disruption of the exofacial sugar-binding sites on the glucose-transporter proteins. 相似文献
118.
A polymerase chain reaction mediated by a single primer: cloning of genomic sequences adjacent to a serotonin receptor protein coding region. 总被引:5,自引:2,他引:3 下载免费PDF全文
Under appropriate conditions, specific double-stranded DNA product was generated after amplification of genomic DNA sequences in a polymerase chain-like reaction that contained only a single primer. This type of amplification reaction was performed with a variety of primers and substrate DNAs. In addition to nonspecific heterogeneous products, 5 of 11 primers reproducibly directed synthesis of double-stranded DNA that corresponded to the region of the template that contained the authentic primer annealing site. Three of these amplified products were cloned and their ends were sequenced. All three contained a copy of the primer at both 5' ends, and the position of one of the primers represented the authentic primer binding site. In each case, the location of the second copy of the primer indicated that it had initially hybridized to a partially homologous sequence in the template DNA. This single primer reaction makes it possible to amplify and clone a DNA region of unknown sequence that is adjacent to a known DNA sequence. One of the single primer reaction products described here included sequence to the 5' side of the coding region of a serotonin receptor gene that contained a functional promoter. 相似文献
119.
Curtis J. Condon Su-Hua Chang Albert S. Feng 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1991,168(6):709-725
Summary Response characteristics of 130 single neurons in the superior olivary nucleus of the northern leopard frog (Rana pipiens pipiens) were examined to determine their selectivity to various behaviorally relevant temporal parameters [rise-fall time, duration, and amplitude modulation (AM) rate of acoustic signals. Response functions were constructed with respect to each of these variables. Neurons with different temporal firing patterns such as tonic, phasic or phasic-burst firing patterns, participated in time domain analysis in specific manners. Phasic neurons manifested preferences for signals with short rise-fall times, thus possessing low-pass response functions with respect to this stimulus parameter; conversely, tonic and phasic-burst units were non-selective and possessed all-pass response functions. A distinction between temporal firing patterns was also observed for duration coding. Whereas phasic units showed no change in the mean spike count with a change in stimulus duration (i.e., all-pass duration response functions), tonic and phasic-burst units gave higher mean spike counts with an increase in stimulus duration (i.e., primary-like high-pass response functions). Phasic units manifested greater response selectivity for AM rate than did tonic or phasic-burst units, and many phasic units were tuned to a narrow range of modulation rates (i.e., band-pass). The results suggest that SON neurons play an important role in the processing of complex acoustic patterns; they perform extensive computations on AM rate as well as other temporal parameters of complex sounds. Moreover, the response selectivities for rise-fall time, duration, and AM rate could often be shown to contribute to the differential responses to complex synthetic and natural sounds.Abbreviations
SON
superior olivary nucleus
-
DMN
dorsal medullary nucleus
-
TS
torus semicircularis
-
FTC
frequency threshold curve
-
BF
best excitatory frequency
-
PAM
pulsatile amplitude modulation
-
SAM
sinusoidal amplitude modulation
-
SQAM
square-wave amplitude modulation
-
MTF
modulation transfer function
-
PSTH
peri-stimulus time histogram 相似文献
120.