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   80553篇
  免费   4634篇
  国内免费   82篇
林业   3650篇
农学   2803篇
基础科学   529篇
  10006篇
综合类   12517篇
农作物   3197篇
水产渔业   4106篇
畜牧兽医   41840篇
园艺   951篇
植物保护   5670篇
  2019年   864篇
  2018年   1209篇
  2017年   1334篇
  2016年   1278篇
  2015年   1050篇
  2014年   1297篇
  2013年   3163篇
  2012年   2377篇
  2011年   2725篇
  2010年   1761篇
  2009年   1811篇
  2008年   2684篇
  2007年   2584篇
  2006年   2350篇
  2005年   2263篇
  2004年   2118篇
  2003年   2235篇
  2002年   2090篇
  2001年   2436篇
  2000年   2391篇
  1999年   1906篇
  1998年   763篇
  1997年   826篇
  1995年   905篇
  1994年   761篇
  1993年   767篇
  1992年   1555篇
  1991年   1679篇
  1990年   1653篇
  1989年   1655篇
  1988年   1541篇
  1987年   1495篇
  1986年   1564篇
  1985年   1489篇
  1984年   1297篇
  1983年   1094篇
  1982年   773篇
  1979年   1202篇
  1978年   905篇
  1977年   856篇
  1976年   814篇
  1975年   846篇
  1974年   1052篇
  1973年   1085篇
  1972年   1037篇
  1971年   968篇
  1970年   950篇
  1969年   909篇
  1968年   763篇
  1967年   855篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
991.
Small breed dogs (<15 kg) affected by cranial cruciate ligament rupture secondary to cranial cruciate ligament disease are usually middle-aged (mean age at presentation: 5.4 to 9.8 years); terrier breeds, miniature and toy poodles are over-represented. Small breed dogs have a different morphology of the proximal tibia compared to medium and large breed dogs with a steep tibial plateau angle (mean tibial plateau angle 28.8° to 36.3°), absent base of the flare of the tibial tuberosity and a caudally bowed fibula. There is a lack of evidence regarding the optimal management of cranial cruciate ligament rupture in small dogs. The treatment options consist of conservative management, extracapsular stabilisation, cranial closing wedge ostectomy, tibial plateau levelling osteotomy and tibial tuberosity advancement. The limited evidence available shows that conservative management is likely to result in prolonged recovery time (average time to recovery approximately 4 months). There is paucity of reports focussing on extracapsular stabilisation in small breed dogs, and questions have been raised regarding the early failure of the extracapsular suture subject to higher loads due to the steep tibial plateau angle of small breed dogs. Cranial closing wedge ostectomy and tibial plateau levelling osteotomy have been reported to have low major complication rates and good subjective outcomes. It is controversial whether tibial tuberosity advancement is a suitable technique in dogs with steep tibial plateau angle, which includes most small breed dogs.  相似文献   
992.
993.
The use of live animals for educational purposes is an old practice that is still employed in teaching and research institutions. However, there are several objections to this practice, whether for ethical or humanitarian reasons. Surgical techniques teaching using anatomical pieces and/or preserved cadavers promotes greater learning efficiency, provides exercise repetition and increases the confidence and satisfaction of the students when compared to the use of live animals. The current work aimed to analyse the feasibility of using fresh swine urinary bladder and small intestines (jejunum), obtained from slaughterhouses, fixed in 99.8% ethyl alcohol (EA) and preserved in sodium chloride hypersaturated solution (SCHS) at 30%, for 7, 14 and 21 days, as an alternative method for surgical skills training (SST). Swine viscera, fixed in EA and preserved in SCHS, presented a realistic appearance, absence of odour and maintained the viable morphological characteristics during the performance of the operative techniques. Preservation solutions had low cost, were easy to acquire and did not offers risks to human health. Therefore, urinary bladders and small intestines fixed in 99.8% EA for 30 days and maintained in 30% SCHS at different periods were demonstrated as a good viable option as a preservation method for surgical skills training.  相似文献   
994.
In the present study, the location, histology and number of corpuscles of Stannius (Sc), which are endocrine glands associated with the kidneys of teleost fish, were investigated for the first time in Lake Van fish (Alburnus tarichi), an anadromous and endemic inhabiting Turkey's Lake Van Basin. The Sc, which were ovoid or spheroid and white or cream in colour, were found to vary in number between three and five among the examined fish. The glands were located in the caudal part of the kidney, and either partially or completely embedded, and found to be present on both the ventral and dorsal surface of either side of the caudal part of the kidney. The Sc were surrounded by a connective tissue capsule that penetrated and divided the gland into incomplete lobules. Two types of cells were determined in the parenchyma of the gland. Type-I cells were predominant throughout the parenchyma and larger than the second (type-II). In the type-I cells, the cytoplasm was observed as weakly or moderately eosinophilic with haematoxylin and eosin staining and weakly or moderately acidophilic with Mallory's triple staining. In the type-I cells, the cytoplasm exhibited weak to moderate periodic acid-Schiff staining and slight or uniform staining with aldehyde fuchsin. The type-II cells were round, had a darkly stained spherical nucleus and were dispersed among the type-I cells. They displayed no cytoplasmic staining with the abovementioned stains.  相似文献   
995.
996.
997.
998.
999.
1000.
The aim of this study was to identify differentially expressed genes (DEG) in the Longissimus thoracis muscle of Nelore cattle related to fatty acid (FA) profile through RNA sequencing and principal component analysis (PCA). Two groups of 10 animals each were selected containing PC1 and PC2 extreme DEG values (HIGH × LOW) for each FA group. The intramuscular fat (IMF) was compared between cluster groups by ANOVA, and only the sum of monounsaturated FA (MUFA) and ω3 showed significant differences (p < .05). Interestingly, the highest percentage (95%) of phenotypic variation explained by the sum of the first two PC was observed for ω3, which also displayed the lowest number of DEG (n = 1). The lowest percentage (59%) was observed for MUFA, which also revealed the largest number of DEG (n = 66). Since only MUFA and ω3 exhibited significant differences between cluster groups, we can conclude that the differences observed for the remaining groups are not due to the percentage of IMF. Several genes that have been previously associated with meat quality and FA traits were identified as DEG in this study. The functional analysis revealed one KEGG pathway and eight GO terms as significant (p < .05), in which we highlighted the purine metabolism, glycolytic process, adenosine triphosphate binding and bone development. These results strongly contribute to the knowledge of the biological mechanisms involved in meat FA profile of Nelore cattle.  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