全文获取类型
收费全文 | 34129篇 |
免费 | 2909篇 |
国内免费 | 1773篇 |
出版年
2023年 | 332篇 |
2022年 | 382篇 |
2021年 | 1463篇 |
2020年 | 1032篇 |
2019年 | 1248篇 |
2018年 | 1224篇 |
2017年 | 863篇 |
2016年 | 1324篇 |
2015年 | 2022篇 |
2014年 | 2363篇 |
2013年 | 2547篇 |
2012年 | 3082篇 |
2011年 | 2762篇 |
2010年 | 1718篇 |
2009年 | 1428篇 |
2008年 | 1661篇 |
2007年 | 1513篇 |
2006年 | 1350篇 |
2005年 | 1141篇 |
2004年 | 1019篇 |
2003年 | 864篇 |
2002年 | 743篇 |
2001年 | 674篇 |
2000年 | 680篇 |
1999年 | 652篇 |
1998年 | 376篇 |
1997年 | 325篇 |
1996年 | 351篇 |
1995年 | 333篇 |
1994年 | 325篇 |
1993年 | 217篇 |
1992年 | 351篇 |
1991年 | 270篇 |
1990年 | 305篇 |
1989年 | 257篇 |
1988年 | 189篇 |
1987年 | 170篇 |
1986年 | 152篇 |
1985年 | 134篇 |
1984年 | 121篇 |
1983年 | 95篇 |
1982年 | 77篇 |
1981年 | 60篇 |
1980年 | 45篇 |
1979年 | 74篇 |
1978年 | 54篇 |
1977年 | 52篇 |
1975年 | 59篇 |
1974年 | 47篇 |
1973年 | 50篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
31.
Behavioral and reproductive effects of ultrasound on the Indian meal moth, Plodia interpunctella 总被引:1,自引:0,他引:1
Fangneng Huang & Bhadriraju Subramanyam 《Entomologia Experimentalis et Applicata》2004,113(3):157-164
The daily activity patterns of adult movement, female calling, and mating of the Indian meal moth, Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae), were examined both in the absence and presence of ultrasound. Moths were exposed to ultrasound from a commercial ultrasonic device (Cix 0600) that produces constant sound patterns, and from a device developed at Kansas State University (KSU device) that produces random sound patterns. Daily activity patterns of adult movement, female calling, and mating followed a similar trend in the absence or presence of ultrasound. Female calling and mating, both in the absence and presence of ultrasound, primarily occurred during scotophase (21.00–07.00 hours). Ultrasound from the two devices significantly reduced the frequency of female calling and mating relative to unexposed moths. Consequently, the number of spermatophores transferred by males to females and egg production were lower in females exposed to ultrasound compared with unexposed females. In the absence of ultrasound, female P. interpunctella mated 2.9 times, resulting in 2.8 spermatophores/female. In the presence of ultrasound from the Cix 0600 device, a female mated 2.1 times and had 1.7 spermatophores. Corresponding values for the KSU device were 1.9 and 1.4, respectively. In the absence of ultrasound, 78% of the matings lasted 30–90 min, whereas in the presence of ultrasound 45–58% of the matings lasted either less than 30 min or more than 90 min. Moths exposed to ultrasound laid 96–130 eggs female?1 compared with 229 eggs female?1 for unexposed moths. Ultrasound did not affect the pre‐oviposition period and adult longevity of P. interpunctella. 相似文献
32.
33.
34.
Four new hetisine‐type C20‐diterpenoid alkaloids, named as coreanines A–D ( 1 – 4 ), were isolated from the roots of Aconitum coreanum, together with thirteen known alkaloids ( 5 – 17 ). Their structures were elucidated by extensive spectroscopic methods including IR, HR‐ESI‐MS and NMR techniques. All the isolated compounds were screened for the acetylcholinesterase (AChE) inhibitory effects, and none of them showed considerable inhibitory activity. 相似文献
35.
36.
The migration of Schwann cells is critical for development of peripheral nervous system and is essential for regeneration and remyelination after nerve injury. Although several factors have been identified to regulate Schwann cell migration, intrinsic migratory properties of Schwann cells remain elusive. In this study, based on time-lapse imaging of single isolated Schwann cells, we examined the intrinsic migratory properties of Schwann cells and the molecular cytoskeletal machinery of soma translocation during migration. We found that cultured Schwann cells displayed three motile phenotypes, which could transform into each other spontaneously during their migration. Local disruption of F-actin polymerization at leading front by a Cytochalasin D or Latrunculin A gradient induced collapse of leading front, and then inhibited soma translocation. Moreover, in migrating Schwann cells, myosin II activity displayed a polarized distribution, with the leading process exhibiting higher expression than the soma and trailing process. Decreasing this front-to-rear difference of myosin II activity by frontal application of a ML-7 or BDM (myosin II inhibitors) gradient induced the collapse of leading front and reversed soma translocation, whereas, increasing this front-to-rear difference of myosin II activity by rear application of a ML-7 or BDM gradient or frontal application of a Caly (myosin II activator) gradient accelerated soma translocation. Taken together, these results suggest that during migration, Schwann cells display malleable motile phenotypes and the extension of leading front dependent on F-actin polymerization pulls soma forward translocation mediated by myosin II activity. 相似文献
37.
Huang , P. C. (California Inst. Technol., Pasadena), and E. F. Paddock . The time and site of the semidominant lethal action of “Wo” in Lycopersicon esculentum. Amer. Jour. Bot. 49(4): 388–393. Illus. 1962.—The semidominant lethal gene, Wo (Woolly), in Lycopersicon esculentum has been investigated with specific attention to its lethal action. The primary lethal action is believed to occur prior to the torpedo stage of embryonic development (approximately 22 days after anthesis). The presumed WoWo embryos cease to grow before any cambial differentiation or organogenesis can be recognized. Their accompanying endospermous cells, however, continue to divide, this resulting in full-sized seeds. The death of these embryos probably occurs near the time of maturation of the seeds (approximately 52 days after anthesis or when the ovulary turns orange-red). The mechanism of death of the embryo apparently lies in and is specific to the embryo; hence, this is a case of autogenously determined embryonic lethality. 相似文献
38.
Li Zhang Shan Lei Hui Xie Qianqian Li Shuo Liu Qiang Liu Weijin Huang Xinyue Xiao Youchun Wang 《中国病毒学》2020,35(2):235-239
正Dear Editor,Marburg virus(MARV) belongs to the Filoviridae family,along with the related Ebola virus(EBOV). Although MARV is less renowned than EBOV, it causes an equally devastating disease, with clinical symptoms similar to EBOV infection and a remarkably high mortality rate. To 相似文献
39.
Chong Gang-Gang Huang Xiao-Jun Di Jun-Hua Xu Dao-Zhu He Yu-Cai Pei Ya-Nan Tang Ya-Jie Ma Cui-Luan 《Bioprocess and biosystems engineering》2018,41(4):501-510
Bioprocess and Biosystems Engineering - Based on the Prussian blue spectrophotometric method, one high-throughput screening strategy for screening lignin-degrading microorganisms was built on... 相似文献
40.
Following injections of the insoluble portion of disrupted yeast cells ofBlastomyces dermatitidis animals exhibited a biphasic pyrogenic response, a decrease in total serum proteins, and there was no release of interferon. 相似文献