首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   433篇
  免费   53篇
林业   13篇
农学   13篇
基础科学   5篇
  60篇
综合类   44篇
农作物   21篇
水产渔业   38篇
畜牧兽医   256篇
园艺   8篇
植物保护   28篇
  2023年   3篇
  2022年   6篇
  2021年   9篇
  2020年   9篇
  2019年   24篇
  2018年   18篇
  2017年   23篇
  2016年   18篇
  2015年   15篇
  2014年   21篇
  2013年   31篇
  2012年   22篇
  2011年   34篇
  2010年   19篇
  2009年   18篇
  2008年   11篇
  2007年   20篇
  2006年   19篇
  2005年   4篇
  2004年   14篇
  2003年   14篇
  2002年   13篇
  2001年   14篇
  2000年   6篇
  1999年   7篇
  1998年   3篇
  1997年   5篇
  1996年   4篇
  1995年   7篇
  1994年   7篇
  1993年   7篇
  1992年   13篇
  1991年   7篇
  1990年   2篇
  1989年   3篇
  1987年   5篇
  1986年   5篇
  1985年   3篇
  1984年   2篇
  1982年   2篇
  1980年   2篇
  1979年   3篇
  1978年   2篇
  1976年   1篇
  1975年   1篇
  1974年   1篇
  1973年   1篇
  1972年   2篇
  1969年   1篇
  1966年   1篇
排序方式: 共有486条查询结果,搜索用时 718 毫秒
91.
Objectives: To (1) describe vascular distribution in the grossly intact canine cranial cruciate ligament (CCL) using immunohistochemical techniques specific to 2 components of blood vessels (factor VIII for endothelial cells, laminin for basement membrane); and (2) compare the vascularity in different areas of interest (craniomedial versus caudolateral bands; core versus epiligamentous regions; and proximal versus middle versus distal portions) in the intact normal canine CCL. Study Design: In vitro study. Animals: Large, mature dogs (n=7) of breeds prone to CCL disease that were euthanatized for nonorthopedic conditions. Methods: Intact CCL were collected from fresh canine cadavers free from stifle pathology. CCL tissue was processed for immunohistochemistry and stained for factor VIII and laminin. Vascular density was determined by histomorphometric analysis. Results: Specific vascular staining was sparsely identified throughout the CCL; however, the proximal portion of the CCL appears to have a greater number of vessels than the middle or distal portion of the ligament. Conclusions: The CCL is a hypovascular tissue and its vascular distribution is not homogeneous.  相似文献   
92.

Purpose  

Tessier's sequential extraction method is usually used to study metal parting among different phases in soils. The main objective of this study was to determine the redistribution of trace metals which were added simultaneously to a sandy loam soil by use of the fractional distribution and reduced partition indexes and the risk of assessment code (RAC).  相似文献   
93.
94.
Cataiase, peroxidase and IAA‐oxidase activities, so as odiphenolics content in sunflower leaves grown in hydroponics with 4 B levels (0.05; 0.25; 0.5 and 2.0 ppm) were determined. The biochemical assays were made when visual symptons were clearly developed.

Cataiase activity significantly increased in B deficient leaves. Peroxidase, IAA‐oxidase activities and o‐diphenolics content did not significantly change with B levels. The lag period for IAA‐oxidase activity was significantly reduced in B deficient and toxic leaves with respect to the normal ones. These results are in accordance with the hypothesis that one of the B action could be to enhance cataiase activity, the “in vivo” decrease of H2O2 levels beeing the cause of the variation in other enzymatic activities related with that substrate.  相似文献   

95.
The development of a core collection, one which represents the genetic diversity of a crop with minimal redundancy and increases utility of the collection as a whole, is especially important as the funding for germplasm collections decreases. With limited resources, it is difficult to manage large germplasm collections and disperse genetically diverse germplasm to plant breeders. An algorithm was developed to assist in selection of core collections based on estimates of genetic distance. The criteria for selection of the maximum genetically diverse set were based on rankings of genetic distance between an accession with respect to all other accessions. Depending on the size core which a user wished, a zone around each selected accession was determined and no other accession within these limits was selected. The premise for the algorithm was that the genetic variability represented in the core must be representative of the distribution of genetic distances within the population of interest. In the present study, the algorithm was used with RAPD-marker-based estimates of genetic distance for 270 Theobroma cacao L. accessions and 134 Capsicum accessions that chose a set representing 18.5% of the population and representing the breadth of RAPD-based variation.  相似文献   
96.
A serological survey using indirect immunofluorescence (IFAT) for bovine babesiosis (Babesia bovis and B. bigemina) and card test for anaplasmosis, indicates that these haemoparasites are widespread in Martinique. The high prevalences (62% for B. bovis, 52% for B. bigemina and 43% for Anaplasma marginale) lead to the hypothesis of an unstable epizootic situation for these three haemoparasitic diseases. However, the number of smears examined was too low to evaluate their clinical incidence. Both the American and Cuban card tests gave similar results in the detection of antibodies to A. marginale. Theileria mutans is described for the first time in Martinique. Trypanosomosis (Trypanosoma vivax) has disappeared from Martinique, on clinical and serological evidence.  相似文献   
97.
The bacterial flora of the stomach, small intestine, cecum and bile from 20 healthy opossums (Didelphis virginiana) captured from the wild was studied. Results showed that their gastrointestinal flora was similar to that found in other small mammals but, in addition, opossums are heavily colonized by Salmonella spp., which might adversely affect their adequacy as laboratory animals for some experimental protocols.  相似文献   
98.
The aim was to compare the early luteal development in ewes superovulated with different doses of pFSH. Twenty‐nine Santa Inês ewes received a progesterone device (CIDR®) for 8 days. Gonadotrophic treatment started on Day 6: G200 (control, n = 9, 200 mg); G133 (n = 10, 133 mg); and G100 (n = 10, 100 mg of pFSH). On Day 6, all females received eCG (300 IU). B‐mode and spectral Doppler ultrasonography were performed daily during the early luteal phase (Days 11–15) to monitor the development of corpora lutea (CLs; dimensions) and ovarian arteries indices. CLs were also classified as normal or prematurely regressed (PRCL) on Day 15 by videolaparoscopy. Ewes from G100 and G133 showed gradual increase in luteal diameter during the early luteal phase (p < 0.001), whereas G200 animals presented increase from Day 11 to Day 13, and then decrease on Days 14 and 15 (p < 0.001). The G200 females showed greater percentage of PRCL (45.20%) than those of the other groups (p < 0.001). The normal CLs number was greater in G100 than in G133 (p = 0.04), while the PRCL number was greater in G200 than in the other groups (p = 0.03). Resistive index (RI) was greater in G200 than in G100 (p = 0.02). RI was lower in Day 12 than Day 15 (p = 0.02). Pulsatility index (PI) was greater on Days 14 and 15 (p < 0.01). In conclusion, the lowest dose of pFSH (100 mg) can be considered sufficient for an efficient superovulatory response in sheep, producing better CLs development dynamic in early luteal phase and ovarian blood perfusion and smaller number of PRCL than the traditional (200 mg) pFSH dose.  相似文献   
99.
Commercial embryo transfer (ET) has unprecedented productive and economic implications for the pig sector. However, pig ET has been considered utopian for decades mainly because of the requirements of surgical techniques for embryo collection and embryo deposition into recipients, alongside challenges to preserve embryos. This situation has drastically changed in the last decade since the current technology allows non‐surgical ET and short‐ and long‐term embryo preservation. Here, we provide a brief review of the improvements in porcine ET achieved by our laboratory in the past 20 years. This review includes several aspects of non‐surgical ET technology and different issues affecting ET programmes and embryo preservation systems. The future perspectives of ET technology are also considered. We will refer only to embryos produced in vivo since they are the only type of embryos with possible short‐term use in pig production.  相似文献   
100.
Background: A major,unresolved issue is how the uterine microenvironment determines pregnancy success in cattle.Before implantation,conceptus development depends on the uterine secretome(i.e.,histotroph).Despite its pivotal role,little is known about the dynamics of histotroph synthesis and changes in composition throughout the early diestrus and the relevance to pregnancy establishment.We hypothesize that disturbances on histotroph composition affect the establishment of pregnancy.Aim was to disturb histotroph composition at early diestrus and verify the effects on:(Exp.1) timing to restore its composition; and(Exp.2) pregnancy rate after multiple-embryo transfer.Estrous cycle of multiparous Nelore cows were synchronized and estrus was considered d 0(D0) of the experiments.Disturbance was through flushing each uterine horn with 30 m L of DMPBS and collecting the resulting uterine luminal flushing(ULF) on D1; D4; D7; D1 + D4 + D7.Control group remained not-collected.In Exp.1,ULF was collected on D7.5 from all animals and used for quantification of total protein concentration and abundance of albumin.In Exp.2,three in vitro-produced embryos were transferred to the uterine horn ipsilateral to the ovary containing the CL on D7.5 and pregnancy was checked on D25 by ultrasound.Results: In Exp.1,ULF collection on D4 or D7 increased(1.5-to 2.2-folds) the total protein concentration and albumin abundance.ULF collection on D1 did not alter(P 0.10) these endpoints.In Exp.2,ULF collected on D4 or D7 decreased pregnancy rates to approximately half of that measured in the remaining groups.Conclusions: Subtle perturbations imposed to the native intrauterine milieu,such as those caused by a single,low-volume collection of ULF,profoundly disturbs intrauterine composition and pregnancy success.At least 4 d were necessary for the uterus to recover its composition and the functional capacity to carry post-implantation gestation.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号