全文获取类型
收费全文 | 812篇 |
免费 | 18篇 |
国内免费 | 69篇 |
专业分类
899篇 |
出版年
2015年 | 10篇 |
2013年 | 17篇 |
2012年 | 20篇 |
2011年 | 27篇 |
2010年 | 33篇 |
2009年 | 46篇 |
2008年 | 33篇 |
2007年 | 53篇 |
2006年 | 42篇 |
2005年 | 35篇 |
2004年 | 28篇 |
2003年 | 35篇 |
2002年 | 29篇 |
2001年 | 14篇 |
1999年 | 7篇 |
1998年 | 8篇 |
1997年 | 13篇 |
1996年 | 16篇 |
1995年 | 17篇 |
1993年 | 14篇 |
1992年 | 16篇 |
1991年 | 11篇 |
1990年 | 14篇 |
1989年 | 13篇 |
1988年 | 12篇 |
1987年 | 11篇 |
1986年 | 8篇 |
1985年 | 10篇 |
1984年 | 7篇 |
1983年 | 7篇 |
1981年 | 6篇 |
1980年 | 9篇 |
1978年 | 10篇 |
1977年 | 8篇 |
1976年 | 10篇 |
1975年 | 7篇 |
1974年 | 15篇 |
1973年 | 6篇 |
1972年 | 7篇 |
1971年 | 11篇 |
1966年 | 6篇 |
1959年 | 9篇 |
1958年 | 18篇 |
1957年 | 18篇 |
1956年 | 10篇 |
1955年 | 16篇 |
1954年 | 17篇 |
1953年 | 11篇 |
1952年 | 8篇 |
1951年 | 9篇 |
排序方式: 共有899条查询结果,搜索用时 0 毫秒
31.
The family Embolemidae Westwood, 1833 is recorded for the first time in Korea, based on a species Embolemus ruddii Westwood. A diagnosis of this species complemented by digital images are provided. 相似文献
32.
G. NISHITANI S. NAGAI S. SAKAMOTO C. L. LIAN C. K. LEE T. NISHIKAWA S. ITAKURA M. YAMAGUCHI 《Molecular ecology resources》2007,7(5):827-829
We isolated 15 polymorphic microsatellites from Cochlodinium polykrikoides. These loci provide a class of highly variable genetic markers, as the number of alleles ranged from two to 15, and the estimate of gene diversity was from 0.083 to 0.880 across the 15 microsatellites. We consider that these loci have a potential to reveal the genetic structure and gene flow among C. polykrikoides populations. 相似文献
33.
Summary Proteins synthesized and accumulated during oogenesis or Pseudopotamilla occelata were analyzed by two-dimensional Polyacrylamide gel electrophoresis and fluorography. Significant changes in the patterns of synthesis and accumulation occur during oogenesis, paticularly between previtellogenic and vitellogenic stages, although many of the proteins are represented throughout the process. The changes may be generally dependent upon the variation in the gene expression affecting autosynthesis of proteins. However, appearance of proteins, which occur only at the vitellogenic stages but apparently not synthesized within the oocytes, indicates that heterosynthetic proteins are stage-specifically transported into oocytes. 相似文献
34.
E‐Hyun SHIN Wook‐Gyo LEE Kyu‐Sik CHANG Young‐Mi CHOI Hee‐Il LEE Longzhu JIN Jixu LI Longnan CHEN Dong‐Kyu LEE Chan PARK 《Entomological Research》2011,41(1):36-38
Adult mosquito surveillance was conducted using black light traps in August of 2006 and 2007 at Wangging county and Yanji city, Jilin Province, China to identify the distribution of anopheline mosquitoes in northern China. A total of 2459 female mosquitoes comprising three genera and eight species including Anopheles (Anopheles) lesteri, An. (Ano.) kleini, An. (Ano.) pullus, Culex inatomii, Cx. orientalis, Cx. pipiens, Cx. bitaeniorhynchus and Aedes vexans nipponii were collected. The most commonly collected species was An. kleini which had not been previously reported from China. Anopheles sinensis sensu stricto is commonly collected throughout China, but was not collected from these areas. 相似文献
35.
CHIA‐HUNG HSIEH SIN‐CHE LEE HURNG‐YI WANG 《Zoological Journal of the Linnean Society》2011,161(3):613-632
The phylogeographical patterns of the endemic minnow, Candidia barbatus, were examined using mitochondrial (mt) cytochrome b sequences, allozyme electrophoresis, and morphology. The 23 mtDNA haplotypes recovered were grouped into six lineages (A–F). According to a molecular clock of 1.7% per million years, we estimated that the colonization of C. barbatus to Taiwan took place three million years ago with several subsequent vicariance events. In the allozyme analysis, the Bayesian approach partitioned different populations into three clusters, with clusters I, II, and III mainly found in northern, central, and southern Taiwan, respectively. Morphologically, fish from north and south of the Tropic of Cancer had distinct numbers of lateral line scales and were separated into two morphs. The cohabitation of different mtDNA lineages with high allozymic and morphological similarities suggests that interbreeding amongst them is possible. Therefore, in spite of highly differentiated mtDNA, samples from different collecting sites should be considered a single species. Based on the current population distribution and levels of divergence, we propose that both orogenic activities and marine regression during glacial epoch were the two main forces shaping population differentiation of this species. © 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 161 , 613–632. 相似文献
36.
37.
HomopyrimidineoligonucleotidescanbindtothemajorgrooveofduplexDNAathomopurinehomopyrimidinesequences,formingalocaltriplehelix[1—3].TherearesomekindsoftriplexDNA,unimolecularorbimolecularortermoleculartriplexwhichconsistsofoneortwoorthreestrandsofDNA,respe… 相似文献
38.
JAMES H. DEVRIES LLWELLYN M. ARMSTRONG ROBERT J. MACFARLANE LEE MOATS PAUL T. THOROUGHGOOD 《The Journal of wildlife management》2008,72(8):1790-1797
Abstract: Waterfowl nesting in annual croplands has remained a little-known aspect of waterfowl nesting ecology because of the inability of many studies to systematically search this habitat through the nesting season. Where searches have been conducted, they are generally restricted to the period prior to seeding, and many nests found are destroyed by the seeding operation. Consequently, fall-seeded crops have been promoted as an alternative cropping practice that could increase nest survival of waterfowl nesting in croplands. During 1996–1999, we conducted 3–4 complete nest searches on 4,274 ha of cropland, including spring-seeded wheat and barley, winter wheat, and fall rye in southern Saskatchewan, Canada. Using suites of predictive models, we tested hypotheses regarding relative nest abundance and nest survival among crop types and tested the influence of several landscape-scale covariates on these metrics. Apparent nest densities were higher in fall-seeded crops (winter wheat: 0.39 nests/ha, fall rye: 0.25 nests/ha) than in spring-seeded crops (0.03 nests/ha), and nest density in spring-seeded croplands increased with percent cropland and percent wetland habitat in the surrounding landscape. Nest survival was higher in winter wheat (38%) than in either fall rye (18%) or spring-seeded crops (12%), and nest survival in spring-seeded crops increased with relative nest initiation date. Nest survival was unaffected by surrounding landscape characteristics but tended to be higher in years of average wetness. Based on our findings, winter wheat and fall rye have the potential to provide productive nesting habitat for ≥7 species of upland nesting ducks and fall-seeded crops are a conservation tool well suited to highly cropped landscapes. 相似文献
39.
拟澳洲赤眼蜂(Trichogramma confusum)的体长约0.6mm,腹部长度约0.3mm.雌蜂生殖系统(包括卵巢、生殖腔、受精囊及三种附腺)位于腹部后端,约占腹腔的2/3.成熟的卵巢由两条多滋式的卵巢管组成.两条成熟卵巢的端段细长,扭卷成一条疏松索,基部膨大,内脏贮存大量卵粒.成对的侧输卵管较短,分别开口于生殖腔后方的两侧,中输卵管缺如.受精囊呈梨形,开口于生殖腔后方.雌性生殖系统三种附腺中,第一种附腺是成对的,呈锤状,分别连接于生殖腔前方两侧;第二种附腺,腺体呈球状,其前端以短曲的小管通进膨大的贮腺囊,贮腺囊端部成柄状的弯曲小管,连接于产卵管的基部开口处.第三种附腺的腺体呈棒状,前端为细长的小管,开口于第二种附腺贮腺囊的前端.雄性生殖系统由成对的睪丸,输精管、贮精囊、附腺及单一的射精管组成.蛹的早期到后期至成虫期睾丸的形态结构,各有不同变化. 相似文献
40.
蓖麻蚕前胸腺细胞超微结构的变化与蜕皮激素分泌活动的关系 总被引:1,自引:0,他引:1
本研究叙述蓖麻蚕Philosamia cythia ricini四龄及五龄幼虫前胸腺蜕皮激素分泌活动各不同时期所显示的腺细胞超微结构变化.从幼虫蜕皮后至进入眠期之间的腺细胞结构可分为三个时期,(1)不活动期:细胞核呈圆形,核内密布染色质及核仁,细胞质内有结构完整的线粒体、粗面及滑面内质网、核糖体和高尔基氏体;细胞外围的细胞间区内有许多小囊泡及多泡囊.(2)活动期:细胞结构变化为细胞核膜出现内陷、外突,形成波浪形的核周膜;线粒体变形,出现内嵴稀疏的空心线粒体.(3)激素释放期:细胞核变形,形成若干长短不一向外伸出的指状突,有些伸达细胞边缘;其余细胞器退化,其后仅余残缺的高尔基氏体,稀疏的核糖体,线粒体的内崤逐渐消失,成为空腔扩大的及空腔内藏“膜轮”的线粒体,和一些溶解体及大形“膜轮”. 相似文献