全文获取类型
收费全文 | 3395篇 |
免费 | 305篇 |
国内免费 | 287篇 |
出版年
2023年 | 40篇 |
2022年 | 51篇 |
2021年 | 86篇 |
2020年 | 96篇 |
2019年 | 145篇 |
2018年 | 137篇 |
2017年 | 96篇 |
2016年 | 116篇 |
2015年 | 125篇 |
2014年 | 217篇 |
2013年 | 255篇 |
2012年 | 138篇 |
2011年 | 154篇 |
2010年 | 124篇 |
2009年 | 188篇 |
2008年 | 193篇 |
2007年 | 166篇 |
2006年 | 158篇 |
2005年 | 158篇 |
2004年 | 127篇 |
2003年 | 122篇 |
2002年 | 124篇 |
2001年 | 77篇 |
2000年 | 67篇 |
1999年 | 66篇 |
1998年 | 67篇 |
1997年 | 50篇 |
1996年 | 55篇 |
1995年 | 46篇 |
1994年 | 64篇 |
1993年 | 39篇 |
1992年 | 46篇 |
1991年 | 34篇 |
1990年 | 37篇 |
1989年 | 39篇 |
1988年 | 27篇 |
1987年 | 34篇 |
1986年 | 15篇 |
1985年 | 28篇 |
1984年 | 37篇 |
1983年 | 27篇 |
1982年 | 27篇 |
1981年 | 27篇 |
1980年 | 17篇 |
1979年 | 15篇 |
1978年 | 9篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1975年 | 5篇 |
1973年 | 4篇 |
排序方式: 共有3987条查询结果,搜索用时 15 毫秒
1.
Giovana Duarte Viana Rodrigues João Paulo Felix Augusto de Almeida Tamí Mott 《Studies on Neotropical Fauna and Environment》2017,52(3):204-215
Herein, we provide external and internal morphological data of Scinax skuki tadpoles from its type locality. The benthic tadpole of S. skuki has eyes and nostrils positioned dorsally, vent tube dextral and reaching the free margin of the ventral fin, oral disk ventral with posterior margin concave when partially closed, labial tooth row formula 2/3, and the presence of nonpigmented spurs behind the lower jaw. These characters, together with the absence of a tectum parietale, and the shapes of the pars articularis quadrati and suprarostral, are useful for species identification and may be informative for systematic purposes. 相似文献
2.
3.
Improved two‐stage group sequential procedures for testing a secondary endpoint after the primary endpoint achieves significance 下载免费PDF全文
Huiling Li Jianming Wang Xiaolong Luo Janis Grechko Christopher Jennison 《Biometrical journal. Biometrische Zeitschrift》2018,60(5):893-902
In two‐stage group sequential trials with a primary and a secondary endpoint, the overall type I error rate for the primary endpoint is often controlled by an α‐level boundary, such as an O'Brien‐Fleming or Pocock boundary. Following a hierarchical testing sequence, the secondary endpoint is tested only if the primary endpoint achieves statistical significance either at an interim analysis or at the final analysis. To control the type I error rate for the secondary endpoint, this is tested using a Bonferroni procedure or any α‐level group sequential method. In comparison with marginal testing, there is an overall power loss for the test of the secondary endpoint since a claim of a positive result depends on the significance of the primary endpoint in the hierarchical testing sequence. We propose two group sequential testing procedures with improved secondary power: the improved Bonferroni procedure and the improved Pocock procedure. The proposed procedures use the correlation between the interim and final statistics for the secondary endpoint while applying graphical approaches to transfer the significance level from the primary endpoint to the secondary endpoint. The procedures control the familywise error rate (FWER) strongly by construction and this is confirmed via simulation. We also compare the proposed procedures with other commonly used group sequential procedures in terms of control of the FWER and the power of rejecting the secondary hypothesis. An example is provided to illustrate the procedures. 相似文献
4.
Patch assessment in foraging flocks of European starlings: evidence for the use of public information 总被引:8,自引:4,他引:4
A field experiment was carried out to determine whether group-foragingstarlings (Sturnus vulgaris) use public information to helpthem estimate the quality of an artificial resource patch anddepart accordingly. Three kinds of information are potentiallyavailable in a group: patch-sample information, pre-harvestinformation, and public information. These three types of informationcan be combined into four patch assessment strategies: (1) patch-samplealone; (2) patch-sample and pre-harvest; (3) patch-sample andpublic; and (4) patch-sample, pre-harvest, and public. Dependingon the foraging environment we presented to the starlings, eachassessment strategy made a unique set of predictions concerningthe patch departure decisions of pairs of birds based on differencesin their foraging success. The environment was manipulated intwo ways: by altering the variability in patch quality and bychanging compatibility, the ease with which individual birdscould simultaneously acquire both patch-sample and public information.Our observations on patch persistence and departure order demonstratethat the starlings used a combination of patch-sample and publicinformation, but not pre-harvest information, to estimate thequality of the experimental patch. Moreover, our results suggestthat starlings use public information only when it is easilyavailable and ignore it under incompatible conditions. Thisstudy provides the first evidence of public information usein a patch assessment problem. 相似文献
5.
Yeon‐Sook Kim Yeon‐Joo Choi Kyung‐Min Lee Kyu‐Joong Ahn Heung‐Chul Kim Terry Klein Ju Jiang Allen Richards Kyung‐Hee Park Won‐Jong Jang 《Microbiology and immunology》2017,61(7):258-263
6.
Reindeer habitat use in relation to two small wind farms,during preconstruction,construction, and operation 下载免费PDF全文
Worldwide there is a rush toward wind power development and its associated infrastructure. In Fennoscandia, large‐scale wind farms comprising several hundred windmills are currently built in important grazing ranges used for Sámi reindeer husbandry. In this study, reindeer habitat use was assessed using reindeer fecal pellet group counts in relation to two relatively small wind farms, with 8 and 10 turbines, respectively. In 2009, 1,315 15‐m2 plots were established and pellet groups were counted and cleaned from the plots. This was repeated once a year in May, during preconstruction, construction, and operation of the wind farms, covering 6 years (2009–2014) of reindeer habitat use in the area. We modeled the presence/absence of any pellets in a plot at both the local (wind farm site) and regional (reindeer calving to autumn range) scale with a hierarchical logistic regression, where spatial correlation was accounted for via random effects, using vegetation type, and the interaction between distance to wind turbine and time period as predictor variables. Our results revealed an absolute reduction in pellet groups by 66% and 86% around each wind farm, respectively, at local scale and by 61% at regional scale during the operation phase compared to the preconstruction phase. At the regional, scale habitat use declined close to the turbines in the same comparison. However, at the local scale, we observed increased habitat use close to the wind turbines at one of the wind farms during the operation phase. This may be explained by continued use of an important migration route close to the wind farm. The reduced use at the regional scale nevertheless suggests that there may be an overall avoidance of both wind farms during operation, but further studies of reindeer movement and behavior are needed to gain a better understanding of the mechanisms behind this suggested avoidance. 相似文献
7.
L. Marklund M. Johansson U. Gustafsson L. Andersson A. K. Winterö M. Fredholm P. D. Thomsen 《Animal genetics》1993,24(5):333-338
Restriction fragment length polymorphisms (RFLPs) were described for the porcine loci for β-glucosidase (GBA) and the β-polypeptide 1 of the Na+, K+-transporting ATPase (ATP1B1). Linkage analyses using a three-generation pedigree provided evidence for the assignment of ATP1B1, GBA and two microsatellite loci (S0001 and S0067) to a previously described linkage group comprising the loci for blood group L (EAL) and an anonymous microsatellite (S0097). The linear order of the six markers was determined with confidence by multipoint analyses and the length of the linkage group was estimated at 88 CM. This linkage group was assigned to pig chromosome 4 on the basis of a previous physical localization of the ATP1B1 gene. In situ hybridization data for S0001 presented in this study were consistent with a localization on chromosome 4 and suggested a regional localization to 4pl2-pl3. The present study reveals conflicting data concerning the genetic localization of the K88 loci controlling the expression of the receptors for the E. coli pilus antigens. One group has reported data suggesting a loose linkage between K88 and EAL, now mapped to chromosome 4, whereas two other groups have found linkage between K88 and the transferrin locus (TF), mapped to chromosome 13 by in situ hybridization. 相似文献
8.
9.
10.