全文获取类型
收费全文 | 4902篇 |
免费 | 381篇 |
国内免费 | 1篇 |
出版年
2023年 | 33篇 |
2022年 | 49篇 |
2021年 | 129篇 |
2020年 | 86篇 |
2019年 | 128篇 |
2018年 | 174篇 |
2017年 | 154篇 |
2016年 | 187篇 |
2015年 | 263篇 |
2014年 | 260篇 |
2013年 | 377篇 |
2012年 | 368篇 |
2011年 | 395篇 |
2010年 | 265篇 |
2009年 | 224篇 |
2008年 | 232篇 |
2007年 | 239篇 |
2006年 | 176篇 |
2005年 | 161篇 |
2004年 | 139篇 |
2003年 | 131篇 |
2002年 | 113篇 |
2001年 | 93篇 |
2000年 | 112篇 |
1999年 | 77篇 |
1998年 | 54篇 |
1997年 | 27篇 |
1996年 | 29篇 |
1995年 | 26篇 |
1994年 | 17篇 |
1993年 | 17篇 |
1992年 | 27篇 |
1991年 | 27篇 |
1990年 | 19篇 |
1989年 | 26篇 |
1988年 | 17篇 |
1987年 | 16篇 |
1986年 | 31篇 |
1985年 | 19篇 |
1984年 | 31篇 |
1983年 | 28篇 |
1982年 | 23篇 |
1981年 | 15篇 |
1980年 | 38篇 |
1979年 | 29篇 |
1978年 | 29篇 |
1977年 | 26篇 |
1976年 | 14篇 |
1974年 | 12篇 |
1973年 | 12篇 |
排序方式: 共有5284条查询结果,搜索用时 31 毫秒
1.
2.
Oussama El Far Béatrice Marquèze Christian Leveque Nicole Martin-Moutôt Bethan Lang John Newsom-Davis †Akira Yoshida †Masami Takahashi Michael J. Seagar 《Journal of neurochemistry》1995,64(4):1696-1702
Abstract: In Lambert-Eaton myasthenic syndrome neurotransmitter release is reduced by an autoimmune response directed against the calcium channel complex of the nerve terminal. Autoantibodies were detected by immunoprecipitation assays using solubilized receptors labeled with ligands selective for N-type (125 I-ω conotoxin GVIA) and L-type ([3 H]PN200-110) calcium channels. Sera with a high antibody titer (>3 n M ) against rat brain N-type channels contained autoantibodies that immunoprecipitated neuronal and muscle L-type channels. These IgG fractions stained a 55-kDa protein in immunoblots of purified skeletal muscle dihydropyridine receptor, suggesting that they contain autoantibodies against the β subunit of the calcium channel. A distinct antibody population in the same fractions reacted with a nerve terminal 65-kDa protein that is unrelated to the β subunit and displays properties similar to those of synaptotagmin. 相似文献
3.
AbstractA study was undertaken to compare the patterns of spatial variability, epiphytic percentage cover, and distribution of epiphytic fauna and flora between the two adjacent seagrasses Cymodocea nodosa and the invasive species Halophila stipulucea. Samples were taken at six stations separated by 600?m and exposed to different current conditions. The stations G2 and G5 were affected by a high current tide, while G4 was directly exposed to the northern marine currents. The station G3 was situated in the middle of a Posidonia oceanica bed and was less exposed to hydrodynamism, whereas the other stations were relatively protected. Results indicate that for both H. stipulacea and C. nodosa, shoot density and epiphytic cover biomass decreased when exposed to high levels of hydrodynamic activity. In terms of epiphytic leaf assemblages, our results showed significant differences for the two host plants in their mean cover and for the six stations at the largest and smallest spatial scale. Our observations highlight the dominance of Rhodophyta and the low number of epiphytic species and the epiphytic cover on H. stipulacea compared to C. nodosa. In addition, results indicate the absence of two taxa Hydrozoans and Annelida in the epiphytic assemblage of H. stipulacea leaves. 相似文献
4.
Activity of salivary glands in secreting honey‐elaborating enzymes in two subspecies of honeybee (Apis mellifera L) 下载免费PDF全文
Aliaa A. Al‐Sherif Adel M. Mazeed Mohamed A. Ewis Emad A. Nafea El‐Seid E. Hagag Ahmed A. Kamel 《Physiological Entomology》2017,42(4):397-403
The activity of invertase, glucose oxidase and amylase in the cephalic (post‐cerebral) and thoracic salivary glands is determined in Egyptian and Carniolan honeybees (Apis mellifera L). For this purpose, three ages of worker bees are selected for enzyme assays. The results show that the three target enzymes are detected in the two glands during the three worker ages, except invertase, which cannot be detected in the cephalic gland of newly emerged bees of both subspecies. In both glands, the secretion of invertase is highest, followed by amylase and then glucose oxidase. In Carniolan bees, invertase secretion of the cephalic and thoracic glands increases gradually with age. In Egyptian bees, invertase increases with age only in the cephalic gland, whereas, in the thoracic gland, the highest secretion activity is detected in 10–15‐day‐old bees. The highest amounts of glucose oxidase and amylase in the cephalic gland are detected in newly emerged individuals of both Egyptian and Carniolan bees. In the thoracic gland, however, the highest activity of both enzymes is recorded only in newly emerged Egyptian bees. The results are discussed in the light of bee management and biological aspects of the two subspecies. 相似文献
5.
Mohamed M. Eid Samy I. El-Kowrany Ahmad A. Othman Dina I. El Gendy Eman M. Saied 《The Korean journal of parasitology》2015,53(1):51-58
Toxocariasis is a soil-transmitted helminthozoonosis due to infection of humans by larvae of Toxocara canis. The disease could produce cognitive and behavioral disturbances especially in children. Meanwhile, in our modern era, the incidence of immunosuppression has been progressively increasing due to increased incidence of malignancy as well as increased use of immunosuppressive agents. The present study aimed at comparing some of the pathological and immunological alterations in the brain of normal and immunosuppressed mice experimentally infected with T. canis. Therefore, 180 Swiss albino mice were divided into 4 groups including normal (control) group, immunocompetent T. canis-infected group, immunosuppressed group (control), and immunosuppressed infected group. Infected mice were subjected to larval counts in the brain, and the brains from all mice were assessed for histopathological changes, astrogliosis, and IL-5 mRNA expression levels in brain tissues. The results showed that under immunosuppression, there were significant increase in brain larval counts, significant enhancement of reactive gliosis, and significant reduction in IL-5 mRNA expression. All these changes were maximal in the chronic stage of infection. In conclusion, the immunopathological alterations in the brains of infected animals were progressive over time, and were exaggerated under the effect of immunosuppression as did the intensity of cerebral infection. 相似文献
6.
7.
Aoumeur Baaliouamer Brahim Y. Merlati 《Bioscience, biotechnology, and biochemistry》2013,77(8):2111-2114
Candida catenulata CBS 1904, the previous type strain of C. ravautii, was selected as the best strain for the production of threo-Os-isocitric acid from water-insoluble carbon sources, non-carbohydrates. The addition of surfactants, lipophilic polyoxyethylene nonyl phenyl ethers, was essential for the acid production, because the cell surface of the strain was less lipophilic. «-Alkanes, ranging from Cn to Cl4, gave the acid in high yields. The acid was produced in ajar fermentor in an about 90% yield on a weight basis as to «-tetradecane supplied. The acid was easily recovered, as crystals of its monopotassium salt, from the concentrated culture broth filtrate. 相似文献
8.
The vegetables germplasm conservation programme in Poland was started in 1982, activities under this program resulted up to
this date in building up a tomato germplasm collection of 782 accessions that are available for distribution to breeders and
researchers in Poland and abroad. Between 1990 and 1999 we distributed 651 tomato seed samples to breeders and scientists
in Poland, and 95 samples to users abroad. During 1990 – 1999 the 652 tomato accessions were evaluated for 43 traits of plants
and fruits. Work is in progress to expand the collection and identify useful characteristics of the collected material, and
to make use of them in breeding and other research works. 相似文献
9.
10.
The estrogen of the doum palm kernel and pollen grains has been isolated as the p,p′-nitrophenylazo benzoyl derivative and identified as estrone. 相似文献