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   132465篇
  免费   7269篇
  国内免费   93篇
林业   5381篇
农学   4269篇
基础科学   831篇
  17037篇
综合类   21482篇
农作物   5393篇
水产渔业   6689篇
畜牧兽医   67961篇
园艺   1801篇
植物保护   8983篇
  2020年   1177篇
  2019年   1375篇
  2018年   2031篇
  2017年   2330篇
  2016年   2095篇
  2015年   1742篇
  2014年   2224篇
  2013年   5290篇
  2012年   4114篇
  2011年   5093篇
  2010年   3245篇
  2009年   3389篇
  2008年   4971篇
  2007年   4666篇
  2006年   4353篇
  2005年   4088篇
  2004年   3851篇
  2003年   3973篇
  2002年   3543篇
  2001年   4150篇
  2000年   4252篇
  1999年   3373篇
  1998年   1474篇
  1997年   1387篇
  1996年   1288篇
  1995年   1529篇
  1994年   1358篇
  1993年   1231篇
  1992年   2584篇
  1991年   2700篇
  1990年   2591篇
  1989年   2611篇
  1988年   2368篇
  1987年   2348篇
  1986年   2427篇
  1985年   2340篇
  1984年   1881篇
  1983年   1678篇
  1982年   1149篇
  1979年   1748篇
  1978年   1397篇
  1977年   1151篇
  1976年   1212篇
  1975年   1292篇
  1974年   1500篇
  1973年   1514篇
  1972年   1405篇
  1971年   1304篇
  1970年   1251篇
  1969年   1283篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.

Background

The study aimed at examining hypoxia-inducible factor (HIF)1α expression in adenocarcinomas and adenomas in bitches in regard to tumour malignancy grade, proliferation, apoptosis and vascularisation. Therefore, paraffin sections of 15 adenomas and 64 adenocarcinomas sampled from 79 dogs aged 6 to 16 years were analysed.

Results

A significantly higher HIF-1α expression was noted in adenocarcinomas in comparison to adenomas (P < 0.0004). Moreover, HIF-1α expression in adenocarcinomas correlated positively with tumour malignancy grade (r = 0.59, P < 0.05), Ki-67 antigen expression (r = 0.43; P < 0.0005), TUNEL-positive cells (r = 0.62, P < 0001) and tumour vascularity measured by quantification of vessels characterized by the expression of von Willebrand Factor (r = 0.57, P < 0.05).

Conclusion

Results of this study indicate a similar biological role of HIF-1α in dogs and in humans, which may confirm suitability of the animal model in investigations on progression of tumours in humans.  相似文献   
993.
1. A number of factors causing variability in the percentages of cracked, and dirty eggs and weekly standard margin (WSM) of returns from eggs over production costs were examined on an integrated commercial poultry plant in Scotland.

2. As the bird aged, the percentage of cracked eggs increased (P <0.01) and the percentage of grade A eggs and WSM decreased (P <0.01). Cracks in dirty eggs (10.1%) were more than double those in all eggs laid (4.9%).

3. Seasonal effects on percentage cracked eggs and percentage grade A eggs were one‐third the magnitude of those due to age but were significant (P <0.05).

4. Variability in percentage cracked eggs, dirty eggs and WSM accounted for by the factors measured, were 72, 64 and 92% respectively.

5. The variability in WSM was significantly affected by percentage lay, food consumption and age but not by percentage cracked eggs, originally dirty and grade A eggs.

6. Flock management and climate inside the laying house each increased the amount of variability accounted for in the percentage cracked eggs and dirty eggs by at least 10%.  相似文献   

994.
995.
Sodium-potassium activated adenosine triphosphatase activity was found to be almost twice as high in renal medulla as in cortex. Infusion of digoxin, a specific inhibitor of the enzyme, into one renal artery of the dog resulted in unilateral natriuresis, impaired concentrating capacity, and reduction of the enzyme activity in both cortex and medulla. It is suggested that the sodium-potassium adenosine triphosphatase plays an important role in urine concentration mechanisms.  相似文献   
996.
997.
The article provides hands-on advice and scientific background information regarding the management of the equine acute colic patient. It summarizes essential information on the patient's history, clinical examination, and legal aspects. The scope of the history is based on the clinical appearance of the patient. In horses with violent and barely controllable signs of pain, it is limited to colic-associated information such as onset, course and severity of colic signs, and the last time of defecation, as well as prior therapeutic intervention. In these patients, the clinical examination is focussed primarily on the assessment of cardiovascular parameters, rectal temperature, and the patient's behaviour. The nasogastric intubation is an essential part of the examination of a horse with colic to prevent a gastric rupture due to gastric distension. Transrectal palpation is equally important and should always be performed unless there are important reasons to object to this procedure. In most cases, a thorough patient history and clinical examination of an acute colic patient allows the examining veterinarian to make a tentative diagnosis and a prognostic evaluation. This helps with the decision to start a conservative or a surgical therapy. Due to the existing obligatory documentation requirement and the duty to inform patient owners, it is of utmost importance to promptly document one's findings, therapeutic measures, consultations, and information of the patient owner in written form. This supports further therapy and it can also be of relevance in a potentially resulting lawsuit.  相似文献   
998.
999.
The isotype-specific antibody responses of sheep immunised with keyhole limpet hemocyanin by a peripheral route (intramuscular (i.m.) injection) were compared to those induced by immunisation via different mucosal routes: (1) intra-nasal spray; (2) rectal deposition with cholera toxin; (3) injection into the mucosa of the small intestine or rectum. Antigen-specific IgG1 antibodies were induced in the i.m., intra-intestinal and intra-rectal injection groups and in a proportion of the cholera toxin immunised sheep, but not in the intra-nasal immunisation group. IgA was the only antibody isotype detected in serum collected from the intra-nasal immunisation group. No significant differences in serum IgA levels were detected in any of the mucosal immunisation groups as compared to the i.m. injection group. In contrast, analysis of the in vitro antibody profiles secreted by circulating antibody-secreting cells (ASC) revealed significantly higher IgA responses in the supernatants from all mucosal immunisation groups. This suggests that the measurement of antibodies secreted by circulating ASCs may be a better correlate of local mucosal responses in ruminants, as has been previously demonstrated in human studies. In addition to IgG1 and IgA responses, immunisation by direct injection of antigen formulations into the intestinal and rectal mucosa were the only groups to induce consistently high IgG2 antibodies in serum and ASC cultures.  相似文献   
1000.
Preference for goat characteristics was determined from 42 traders in six markets in Pangasinan, an important trading center for goats in Luzon, the Philippines, and analyzed using a hedonic price model to determine whether these characteristics are important price determinants of goats. This information is important to goat raisers to respond to the needs of the local market, and thus to achieve a better price and higher income in goat raising. Meatiness, size, breed, sex and age (in descending order) were the dominant goat characteristics preferred by traders. Meatiness had the largest positive influence on price, with a price premium of US$6.24 (US$1.00 = PhP 53), whereas the age of the animal had the smallest influence at US$3.72. However, size and meatiness are manifestations of good breeds. Therefore, continued efforts to improve breeds in order to produce good quality goats are imperative to cater to market needs. Different characteristics implied different price premiums. Traders offered a higher price premium for better goat characteristics; thus, the improvement of these characteristics could result in higher returns for goat raisers.  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