全文获取类型
收费全文 | 18388篇 |
免费 | 1343篇 |
国内免费 | 288篇 |
专业分类
20019篇 |
出版年
2023年 | 162篇 |
2022年 | 238篇 |
2021年 | 448篇 |
2020年 | 320篇 |
2019年 | 389篇 |
2018年 | 559篇 |
2017年 | 451篇 |
2016年 | 669篇 |
2015年 | 962篇 |
2014年 | 1069篇 |
2013年 | 1274篇 |
2012年 | 1475篇 |
2011年 | 1442篇 |
2010年 | 883篇 |
2009年 | 787篇 |
2008年 | 1023篇 |
2007年 | 990篇 |
2006年 | 867篇 |
2005年 | 826篇 |
2004年 | 791篇 |
2003年 | 708篇 |
2002年 | 647篇 |
2001年 | 333篇 |
2000年 | 238篇 |
1999年 | 231篇 |
1998年 | 163篇 |
1997年 | 131篇 |
1996年 | 109篇 |
1995年 | 107篇 |
1994年 | 85篇 |
1993年 | 80篇 |
1992年 | 108篇 |
1991年 | 98篇 |
1990年 | 100篇 |
1989年 | 85篇 |
1988年 | 68篇 |
1987年 | 62篇 |
1986年 | 61篇 |
1985年 | 79篇 |
1984年 | 59篇 |
1983年 | 52篇 |
1982年 | 52篇 |
1981年 | 66篇 |
1980年 | 38篇 |
1979年 | 68篇 |
1978年 | 67篇 |
1977年 | 37篇 |
1976年 | 42篇 |
1974年 | 49篇 |
1971年 | 47篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
53.
54.
55.
Maria A. Diuk‐Wasser Gwenaël Vourc'h Paul Cislo Anne Gatewood Hoen Forrest Melton Sarah A. Hamer Michelle Rowland Roberto Cortinas Graham J. Hickling Jean I. Tsao Alan G. Barbour Uriel Kitron Joseph Piesman Durland Fish 《Global Ecology and Biogeography》2010,19(4):504-514
Aim Ixodes scapularis is the most important vector of human tick‐borne pathogens in the United States, which include the agents of Lyme disease, human babesiosis and human anaplasmosis, among others. The density of host‐seeking I. scapularis nymphs is an important component of human risk for acquiring Borrelia burgdorferi, the aetiological agent of Lyme disease. In this study we used climate and field sampling data to generate a predictive map of the density of host‐seeking I. scapularis nymphs that can be used by the public, physicians and public health agencies to assist with the diagnosis and reporting of disease, and to better target disease prevention and control efforts. Location Eastern United States of America. Methods We sampled host‐seeking I. scapularis nymphs in 304 locations uniformly distributed east of the 100th meridian between 2004 and 2006. Between May and September, 1000 m2 were drag sampled three to six times per site. We developed a zero‐inflated negative binomial model to predict the density of host‐seeking I. scapularis nymphs based on altitude, interpolated weather station and remotely sensed data. Results Variables that had the strongest relationship with nymphal density were altitude, monthly mean vapour pressure deficit and spatial autocorrelation. Forest fragmentation and soil texture were not predictive. The best‐fit model identified two main foci – the north‐east and upper Midwest – and predicted the presence and absence of I. scapularis nymphs with 82% accuracy, with 89% sensitivity and 82% specificity. Areas of concordance and discordance with previous studies were discussed. Areas with high predicted but low observed densities of host‐seeking nymphs were identified as potential expansion fronts. Main conclusions This model is unique in its extensive and unbiased field sampling effort, allowing for an accurate delineation of the density of host‐seeking I. scapularis nymphs, an important component of human risk of infection for B. burgdorferi and other I. scapularis‐borne pathogens. 相似文献
56.
Jong Seok Lee Jae Wan Wee Hye Young Lee Hyo Sil An Eock Kee Hong 《Biotechnology and Bioprocess Engineering》2010,15(3):453-459
Hericium erinaceus is a well known edible and medicinal mushroom used in East-Asia. Recently, H. erinaceus has attracted a lot of attention owing to its antitumor, immuno-modulatory, and cytotoxic effect. It has been postulated that the fruiting body of H. erinaceus contains a polysaccharide that is similar to β-D-glucan, which is known to have antitumor activity against Sarcoma 180. However, optimized liquid culture conditions for enhanced polysaccharide productivity have yet to be developed, which is a necessary step for industrial applications. Therefore, the aim of this study was to determine the optimal liquid culture conditions for maximum polysaccharide production. In shake flask cultures, the optimal concentration of ascorbic acid was found to be 2.0 g/L, which prevented the broth from changing color from yellow to black. The optimal culture conditions were determined to be 23°C, 200 rpm, and a 10% inoculum size, at an uncontrolled initial pH. In addition, the modified medium contained 20 g/L glucose, 10 g/L yeast extract, and 2.0 g/L ascorbic acid. The maximum mycelial biomass and exo-polysaccharide (EPS) production in the modified medium containing uracil was 13.43 and 1.26 g/L, respectively. 相似文献
57.
58.
59.
Csillag A. Bourne R. C. Patel Sanjay N. Stewart Michael G. Tömböl Teréz 《Brain Cell Biology》1989,18(3):369-379
Brain Cell Biology - The distribution of GABA-like immunoreactivity (GABA-LI) in the ectostriatal core (Ec) of domestic chicks (one to two days old) was investigated using (1) preembedding GABA... 相似文献
60.
Ramazan Ulus İbrahim Yeşildağ Muhammet Tanç Metin Bülbül Muharrem Kaya Claudiu T. Supuran 《Bioorganic & medicinal chemistry》2013,21(18):5799-5805
4-Amino-N-(4-sulfamoylphenyl)benzamide was synthesized by reduction of 4-nitro-N-(4-sulfamoylphenyl)benzamide and used to synthesize novel acridine sulfonamide compounds, by a coupling reaction with cyclic-1,3-diketones and aromatic aldehydes. The new compounds were investigated as inhibitors of the metalloenzyme carbonic anhydrase (CA, EC 4.2.1.1), and more precisely the cytosolic isoforms hCA I, II and VII. hCA I was inhibited in the micromolar range by the new compounds (KIs of 0.16–9.64 μM) whereas hCA II and VII showed higher affinity for these compounds, with KIs in the range of 15–96 nM for hCA II, and of 4–498 nM for hCA VII. The structure–activity relationships for the inhibition of these isoforms with the acridine–sulfonamides reported here were also elucidated. 相似文献