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   129195篇
  免费   6844篇
  国内免费   88篇
林业   5520篇
农学   4199篇
基础科学   852篇
  15953篇
综合类   22042篇
农作物   4851篇
水产渔业   6494篇
畜牧兽医   66128篇
园艺   1938篇
植物保护   8150篇
  2018年   2649篇
  2017年   2865篇
  2016年   2095篇
  2015年   1446篇
  2014年   1736篇
  2013年   4417篇
  2012年   3454篇
  2011年   4910篇
  2010年   3602篇
  2009年   3472篇
  2008年   4565篇
  2007年   4531篇
  2006年   3547篇
  2005年   3229篇
  2004年   3179篇
  2003年   3208篇
  2002年   2944篇
  2001年   4157篇
  2000年   4323篇
  1999年   3290篇
  1998年   1269篇
  1997年   1213篇
  1996年   1142篇
  1995年   1478篇
  1994年   1312篇
  1993年   1224篇
  1992年   2807篇
  1991年   2960篇
  1990年   2818篇
  1989年   2789篇
  1988年   2648篇
  1987年   2755篇
  1986年   2731篇
  1985年   2610篇
  1984年   2116篇
  1983年   1812篇
  1982年   1209篇
  1979年   1873篇
  1978年   1510篇
  1977年   1352篇
  1976年   1256篇
  1975年   1344篇
  1974年   1698篇
  1973年   1697篇
  1972年   1653篇
  1971年   1489篇
  1970年   1413篇
  1969年   1348篇
  1968年   1136篇
  1967年   1182篇
排序方式: 共有10000条查询结果,搜索用时 359 毫秒
991.
1. Treatment of rapeseed meal with calcium hydroxide suspension decreased the sinapine content by up to 90%. Smaller decreases were obtained by autolysis, steaming and treatment with ammonia.

2. When this treated meal was fed to susceptible ("tainting") hens the concentration of trimethylamine in the eggs was decreased to much less than that required to cause taint.  相似文献   

992.
1. Eighteen diets supplying all combinations of three phosphorus contents (3.1, 4.0 and 4.8 g non‐phytate P/kg) and six vitamin D supplements (37.5 or 150 μg cholecalciferol/kg; or 16 or 24 μg 25‐hydroxy‐cholecalciferol/kg; or 37.5 μg cholecalciferol/kg with either 16 or 24 μg 25‐hydroxycholecalciferol/kg) were fed to 2 880 pullets of two stocks from 64 to 74 weeks of age. The birds were housed in eight light‐proof rooms, four of which had 24‐h light‐dark cycles (16L : 8D) and four had 28‐h cycles (20L : 8D).

2. The dietary treatments had no significant effect upon food intake, egg output, shell thickness, shell deformation or specific gravity of the eggs.

3. The 28‐h cycle reduced mean rate of lay by 4.5%, increased egg weight by 5.8% and increased shell thickness by 9.4%. The proportion of eggs with shell faults revealed on candling was reduced from 4.1 % to 2.8%.

4. It is concluded from this and other sources that decreasing dietary phosphorus or modifying vitamin D supplements may sometimes lead to increases in shell thickness of the order of 1 to 2%, but that these changes are unlikely to result in a measurable reduction in the proportion of cracked eggs late in the laying year.

5. A 28‐h light‐dark cycle results in a longer and more uniform interval between consecutive ovipositions and thus gives reliable increases in shell thickness which are large enough to reduce the proportion of cracked eggs in many practical situations. Whether it is profitable to use an ahemeral cycle will depend upon the relative prices paid for eggs of different sizes.  相似文献   

993.
1. Wheat, triticale 131 or triticale 72‐S could replace up to half the maize in broiler diets without affecting performance. Replacing more of the maize on either an equal nitrogen basis or a weight basis adversely affected performance.

2. Triticale 72‐S appeared to be superior to triticale 131 as a direct replacement for maize, but both grains were inferior to maize as energy sources.  相似文献   

994.
1. The decrease in strength of an egg shell which is known to accompany an increase in the period of time over which a load is applied might come about by either of two mechanisms: a decrease in the strength of the material constituting the strong, outer layer of the mineral shell, or a decrease in the thickness of this layer brought about by deepening of the crevices that are normally present between adjacent crystal columns in the weak, inner layer of the shell.

2. Experiments designed to discriminate between these mechanisms are described: the results indicate the second mechanism.

3. This mechanism offers explanations for various other shell phenomena, including delayed fracture under a static, cyclical or recurrent load.

4. The main implication for the poultry industry is that any external insult to a shell is likely to weaken it by doing damage that is local, internal, irreparable and cumulative, even though it may be invisible from the outside.  相似文献   

995.
996.
A 10-month-old male domestic short-haired cat was examined because of progressive lameness, a broad face with depressed nasal bridge, small ears, corneal clouding, and multiple bone dysplasia. The cat excreted excessive amounts of glycosaminoglycan (a component of connective tissue) in its urine and had evidence of lysosomal storage of glycosaminoglycans in fibroblasts and neurons. Activity of alpha-L-iduronidase, a lysosomal enzyme involved in glycosaminoglycan degradation, was deficient in cultured fibroblasts and leukocytes. The mucopolysaccharidosis was distinct from that seen in Siamese cats in terms of the pathologic changes and the specific enzyme deficiency.  相似文献   
997.
998.
Virus was isolated from semen and fecal samples from a bull with orchitis, testicular degeneration, aspermatogenesis, and loss of libido. Both isolates were classified as picornavirus, bovine enterovirus serotype I, on the basis of physical, chemical, and serologic characteristics. Veterinary practitioners that may suspect viral infection as a cause of bovine infertility should submit both semen and fecal samples for virus isolation and identification.  相似文献   
999.
1000.
An 11-month-old male Miniature Poodle was found to regurgitate small volumes of fluid and food particles due to a diverticulum in the thoracic oesophagus. The diverticulum was removed surgically. Histologically the wall contained extensive scar tissue. Longterm recovery was uneventful and 5 months after surgery the dog is in good health  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