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   165391篇
  免费   9109篇
  国内免费   819篇
林业   6874篇
农学   5032篇
基础科学   1277篇
  19290篇
综合类   33293篇
农作物   6422篇
水产渔业   7484篇
畜牧兽医   83646篇
园艺   2136篇
植物保护   9865篇
  2019年   1568篇
  2018年   2207篇
  2017年   2512篇
  2016年   2299篇
  2015年   2171篇
  2014年   2416篇
  2013年   6146篇
  2012年   4724篇
  2011年   5766篇
  2010年   3875篇
  2009年   3755篇
  2008年   5483篇
  2007年   5113篇
  2006年   4797篇
  2005年   4604篇
  2004年   4433篇
  2003年   4387篇
  2002年   4239篇
  2001年   4978篇
  2000年   4961篇
  1999年   3758篇
  1998年   1641篇
  1997年   1609篇
  1995年   1793篇
  1994年   1641篇
  1993年   1597篇
  1992年   3315篇
  1991年   3618篇
  1990年   3477篇
  1989年   3532篇
  1988年   3252篇
  1987年   3339篇
  1986年   3536篇
  1985年   3317篇
  1984年   2743篇
  1983年   2473篇
  1982年   1655篇
  1981年   1572篇
  1979年   2513篇
  1978年   2017篇
  1977年   1661篇
  1976年   1675篇
  1975年   1714篇
  1974年   2231篇
  1973年   2301篇
  1972年   2246篇
  1971年   2112篇
  1970年   1987篇
  1969年   1842篇
  1967年   1612篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
92.
93.
94.
Four commercially available semiquantitative milk progesterone tests (Ovucheck-Praxistest: Cambridge Veterinary Science/Smith Kline), Progestassay-Milchprogesteron (Pitman-Moore/Janssen), Reprostrip-Progesteron-Schnelltest (Noctech/Albrecht), Enzygnost-Milchprogesteron (IQ, 'Bio' UK/Hoechst Veterin?r) were examined for their accuracy by using them for the determination of progesterone levels of 64 milk samples, i.e. 1556 single assays. Several test series were performed, using codified samples and changing sequences. Three or four test persons respectively, performed the tests independently and classified the samples semiquantitatively. These test results were then compared to the results acquired by measuring the progesterone levels of the same samples by means of an approved quantitative, labor-bound progesterone test (Hormonost: Biolab). These control tests were performed at a specialized routine labor, by different personnel and at a different location. Lastly, in 48 out of the 64 sampled animals the reproductive status could be evaluated clinically and was taken into account as well. Samples yielding high progesterone levels, i.e. greater than or equal to 9 ng/ml were classified correctly in 84.4 to 96.5% of the cases, whereas samples with low levels (less than or equal to 2.5 ng/ml) were classified correctly in 68.8 to 90.0% of the cases only. Samples ranging between this spectrum (greater than 2.5 less than 9 ng/ml) were classified correctly only in 42.1 to 52.6% of the cases. However, this range appears to be of the most interest for the veterinary practitioner since cows in proestrus or early interestrus tend to have mild progesterone levels within these values. On the other hand, clinical findings are often insufficient for a proper diagnosis just in these animals.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
95.
96.
A review of investigations of the functional anatomy of the equine foot is presented. Emphasis is placed on the relationships of structures involved in the major diseases of the foot.  相似文献   
97.
Gold, bronze, and black (normal pigmentation) body colors in Tilapia mossambica are controlled by a single autosomal gene with incomplete dominant gene action: GG fish are black gg fish are gold; Gg fish are bronze. Because gold body color is produced by the recessive genotype, it is easy to produce and to maintain a truebreeding population of gold T. mossambica for commercial purposes. If all other colors are culled, the population will breed true, because gold × gold will always produce 100% gold offspring. The G gene will be a valuable genetic marker for many genetic studies, such as the production of gynogenetic T. mossambica .  相似文献   
98.
In this study, the effects of nitrogen (N) rate (60, 120, 180 and 240 kg N ha?1 applied in three equal dressings at seeding and after the first and second cuttings) and stubble height (7, 14 and 21 cm) on the dry matter (DM) yield, crude protein (CP) content, and CP yield of a sorghum–sudangrass hybrid [Sorghum bicolor (L.) Moench × Sorghum sudanense (Piper) Stapf., cv. Pioneer 988] in the three‐cut system was investigated. The N rate had no significant effect in the first and third cuttings, but in the second cutting DM yields increased significantly with increase in N rate. The highest yield of 9.1 t ha?1 was obtained with 80 kg N ha?1 for the average of 2 years at the second cutting, but no significant difference was found among the 40, 60 and 80 kg N ha?1 rates. CP content and yield were not significantly affected by N rate at the first and third cuttings, but CP content and yield were significantly affected by application of N at the second cutting. Stubble height had a significant effect on CP content at the third cutting. However, it had no significant effect on CP content at the first and second cuttings. Stubble height had a significant effect on the CP yield at the first cutting, but no significant effect on CP yield at the second and third cuttings.  相似文献   
99.
A porcine in vitro fertilization (IVF) system and seminal quality parameters of frozen–thawed boar semen were used to assess the effectiveness of two different thawing rates of frozen boar semen, and to address the question of whether differences between fertility of ejaculates could be predicted in a limited field trial. In the first experiment, two thawing procedures were analysed (37°C, 30 s; 50°C, 12 s) and no differences in sperm quality were found. However, when the procedure was 50°C, 12 s the IVF results showed a higher number of sperm per penetrated oocyte and a near 10 points higher rate of pronuclear formation. In the second experiment, the fertility results obtained in the limited field trial show to be efficient enough for application in a commercial use, especially for three of the employed boars (fertility ≥80%). In this limited study, the conventional seminal parameters are not accurate enough to discriminate good and bad boars in relation to fertility. On the contrary, parameters of in vitro penetrability are more precise to predict subsequent fertilities. As conclusion, the IVF fertilization system seems to be a good tool to evaluate the quality of frozen–thawed boar semen previous to its commercial way, to verify the bank semen storage quality and a good way to assay new sperm freezing procedures, as it is the more precise evaluating method in estimating the potential fertilizing ability.  相似文献   
100.
In summary, peritonitis in the horse is a potentially life-threatening disease that must be treated promptly and aggressively. Therapy should be aimed at reducing systemic shock and hypovolemia, correction of the primary cause, antibiotic and anti-inflammatory therapy, and abdominal drainage and lavage. The prognosis depends on the ability to diagnose and treat the underlying cause and prevent the development of complications. Mortality rates can be as high as 59.7%, with horses developing postoperative peritonitis having a 56% mortality rate. Long-term complications like adhesion formation or internal abscesses may further reduce the survival rate. The prognosis is best determined by an early and quick response to aggressive treatment.  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