全文获取类型
收费全文 | 7014篇 |
免费 | 691篇 |
国内免费 | 2篇 |
出版年
2023年 | 41篇 |
2021年 | 129篇 |
2020年 | 77篇 |
2019年 | 114篇 |
2018年 | 143篇 |
2017年 | 117篇 |
2016年 | 213篇 |
2015年 | 289篇 |
2014年 | 375篇 |
2013年 | 380篇 |
2012年 | 547篇 |
2011年 | 481篇 |
2010年 | 330篇 |
2009年 | 269篇 |
2008年 | 343篇 |
2007年 | 352篇 |
2006年 | 333篇 |
2005年 | 354篇 |
2004年 | 328篇 |
2003年 | 308篇 |
2002年 | 267篇 |
2001年 | 110篇 |
2000年 | 106篇 |
1999年 | 112篇 |
1998年 | 106篇 |
1997年 | 72篇 |
1996年 | 72篇 |
1995年 | 69篇 |
1994年 | 54篇 |
1993年 | 49篇 |
1992年 | 96篇 |
1991年 | 61篇 |
1990年 | 59篇 |
1989年 | 63篇 |
1988年 | 55篇 |
1987年 | 57篇 |
1986年 | 53篇 |
1985年 | 52篇 |
1984年 | 63篇 |
1983年 | 43篇 |
1982年 | 36篇 |
1981年 | 30篇 |
1980年 | 30篇 |
1979年 | 40篇 |
1978年 | 29篇 |
1976年 | 26篇 |
1975年 | 25篇 |
1974年 | 32篇 |
1972年 | 38篇 |
1970年 | 22篇 |
排序方式: 共有7707条查询结果,搜索用时 218 毫秒
11.
Over the past decade, studies on reproductive morphology in the Squamata (snakes and lizards) have expanded tremendously. With the accumulation of these studies and revisions of the terminology based on structural similarities and differences, it is imperative to review the work on tuataras to determine whether the structural organization fits the revised terminology of vertebrates. We investigated the morphology of the male reproductive system in the Tuatara, Sphenodon punctatus (Rhynchocephalia), the sister taxon to the Squamata. Previous studies on the Tuatara used a nomenclature for the testicular ducts different from the current terminology for amniotes. The reproductive system in the Tuatara is consistent with reports in the Squamata. Two rete testis tubules exit the testis within a connective tissue sheath similar to that shown in other squamate species and the protherian Echidna. Each rete testis divides into multiple ductuli efferentes that fuse with the epididymis. The epididymis transitions into the ductus deferens where the sperm become more concentrated into spherical bundles. The ductus deferens enters the cloacal urodeum separately from the ureter. An ampulla ureter or ampulla urogenital papilla was not observed, which differs from previous studies of lepidosaurians. Furthermore, a sexual segment of the kidney (SSK) was not observed, consistent with previous studies on the Tuatara. 相似文献
12.
Alison M. Hamilton 《BMJ (Clinical research ed.)》1954,2(4897):1165-1166
13.
14.
Gemma L. Moir-Meyer John F. Pearson Felicity Lose Rodney J. Scott Mark McEvoy John Attia Elizabeth G. Holliday Paul D. Pharoah Alison M. Dunning Deborah J. Thompson Douglas F. Easton Amanda B. Spurdle Logan C. Walker The Australian National Endometrial Cancer Study Group The Hunter Community Study Studies of Epidemiology Risk Factors in Cancer Heredity 《Human genetics》2015,134(3):269-278
15.
16.
Alison E. Holliday Travis M. Mattingly Neil J. Holliday 《Physiological Entomology》2015,40(2):131-137
Secretions of an eversible gland on the metathorax of larvae of Chlaenius cordicollis Kirby (Coleoptera: Carabidae) are investigated by headspace analysis using solid phase microextraction followed by gas chromatography‐mass spectrometry (GC‐MS). Larvae from Manitoba, Canada and Pennsylvania, U.S.A., are sampled. Nine presumed defensive compounds are detected when the gland is everted, and this represents the first characterization of defensive secretions of larvae of a carabid beetle. With the exception of a single component (2‐methoxy‐4‐methylphenol), these compounds are distinct from those found in the defensive secretion of adult C. cordicollis. However, seven are more oxidized versions of the alkylphenolic compounds secreted by adult beetles: three hydroquinones (hydroquinone, methylhydroquinone and 2,3‐dimethylhydroquinone) and four quinones (p‐benzoquinone, toluquinone, 2,3‐dimethylquinone and ethyl‐p‐benzoquinone). An additional alkoxyphenol (2‐methoxy‐4‐ethylphenol) is also detected. Two patterns of composition are observed: in one, p‐benzoquinone and hydroquinone are undetectable and the ratio of toluquinone : 2,3‐dimethylquinone is 1 : 4.6 ± 0.6 (mean ± SE); in the other, all nine compounds are detectable and the ratio of toluquinone : 2,3‐dimethylquinone is 1 : 1.0 ± 0.2. These differences in pattern do not appear to be related to geographical source, sex or age of the larvae. 相似文献
17.
Tein McDonald 《Ecological Management & Restoration》2004,5(2):87-97
The WildCountry program boldly aims to offer 'a future for Australia's wilderness and biodiversity throughout and beyond the 21st Century'. This is to be achieved through building partnerships — one of the most important being a formal partnership with ecologists. 相似文献
18.
19.
Abstract. Contrary to current assumptions, the reflex blood of two-spot ladybirds, Adalia bipunctata , and seven-spot ladybirds, Coccinella septempunctata , contains haemocyte-like cells. Furthermore, DNA can be extracted and amplified from coccinellid reflex blood, confirming the presence of haemocyte-like cells and demonstrating a nondestructive method of DNA extraction. 相似文献
20.