全文获取类型
| 收费全文 | 313807篇 |
| 免费 | 17080篇 |
| 国内免费 | 673篇 |
专业分类
| 林业 | 24788篇 |
| 农学 | 14285篇 |
| 基础科学 | 2990篇 |
| 47146篇 | |
| 综合类 | 39657篇 |
| 农作物 | 17680篇 |
| 水产渔业 | 18497篇 |
| 畜牧兽医 | 134497篇 |
| 园艺 | 6513篇 |
| 植物保护 | 25507篇 |
出版年
| 2019年 | 3740篇 |
| 2018年 | 4513篇 |
| 2017年 | 4847篇 |
| 2016年 | 5113篇 |
| 2015年 | 4534篇 |
| 2014年 | 5950篇 |
| 2013年 | 16564篇 |
| 2012年 | 8111篇 |
| 2011年 | 10395篇 |
| 2010年 | 8216篇 |
| 2009年 | 8625篇 |
| 2008年 | 9706篇 |
| 2007年 | 9044篇 |
| 2006年 | 9254篇 |
| 2005年 | 8423篇 |
| 2004年 | 8263篇 |
| 2003年 | 8106篇 |
| 2002年 | 7360篇 |
| 2001年 | 8467篇 |
| 2000年 | 8206篇 |
| 1999年 | 7233篇 |
| 1998年 | 4375篇 |
| 1997年 | 4421篇 |
| 1996年 | 4124篇 |
| 1995年 | 4733篇 |
| 1994年 | 4138篇 |
| 1993年 | 3833篇 |
| 1992年 | 5670篇 |
| 1991年 | 5943篇 |
| 1990年 | 5815篇 |
| 1989年 | 5773篇 |
| 1988年 | 5245篇 |
| 1987年 | 5260篇 |
| 1986年 | 5128篇 |
| 1985年 | 5258篇 |
| 1984年 | 4647篇 |
| 1983年 | 4324篇 |
| 1982年 | 3344篇 |
| 1981年 | 3141篇 |
| 1980年 | 3083篇 |
| 1979年 | 4119篇 |
| 1978年 | 3513篇 |
| 1977年 | 3206篇 |
| 1976年 | 3017篇 |
| 1975年 | 2986篇 |
| 1974年 | 3383篇 |
| 1973年 | 3480篇 |
| 1972年 | 3232篇 |
| 1971年 | 3103篇 |
| 1970年 | 3008篇 |
排序方式： 共有10000条查询结果，搜索用时 15 毫秒
921.
Described in this paper are 2 methodological variants for photometric recording of sperm aggregation. Heparin was used to induce aggregation. One of the working principles was related to aggregation-associated alteration of turbidity in an agitated cell suspension, measured by the KZM-1 coagulation-time meter, in analogy to measurement of thrombocyte aggregation. The 2nd variant was based on variation of cloudiness due to sedimentation of aggregates in a non-agitated suspension. Both methods provided equally valid information. They characterised both intensity of aggregation as a combined effect of the number and size of aggregates as well as the rate of aggregation. Photometric recording has proved to be an objectivated method for quantitative assessment of aggregation. Its use is proposed for studies into capacitation or immunological response of spermatozoa. 相似文献
922.
G. C. W. England W. Edward Allen D. J. Porter 《The Journal of small animal practice》1989,30(8):441-443
A two-year-old dog was presented with no scrotal testes. There was no history of castration but at laparotomy no testes were found. To confirm that the dog was truly anorchid a human chorionic gonadotrophin stimulation test was performed. This was then validated in normal entire and castrated dogs. 相似文献
923.
盐分对碱茅种子发芽影响的机制 总被引：15，自引：0，他引：15
耐碱茅种子在盐（NaCl与Na2SO4）及干旱（PEG－6000模拟）胁迫下发芽及其机制的比较研究表明，种子发芽率随溶液渗透势的降低而下降，在等渗条件下三种溶液中的发芽率次序为Na2SO4＞NaCl＞PEG。NaCl与Na2SO4主要通过影响种子吸水量及对膜的毒性影响发芽，根据相关及通径分析结果，其机制为：（1）溶液渗透势及Na+浓度决定的种子吸水对发芽的直接正效应（通径系数0．73）；（2）溶液Na+浓度引起的膜毒性对发芽的直接负效应（－0．51）；（3）种子从溶液中吸收Na使种子吸水增加对发芽的间接正效应（0．30）及使膜毒性增大对发芽的间接负效应（－0．24）。 相似文献
924.
Bull sperm pellets experimentally infected with various concentrations of Mycoplasma (M.) bovis, M. bovigenitalium, and M. californicum were stored several months at -196 degrees C and were subsequently tested for mycoplasmas, using different methods and culturing media. M. bovis was reliably identified by laboratory diagnosis up to a concentration of 10(2) cfu/pellet. M. bovigenitalium and M. californicum were found to make higher demands on the quality of culturing substrates. Recommended are 1-h broth incubation and 5-d broth breeding. 相似文献
925.
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
926.
927.
928.
Smith HM 《Science (New York, N.Y.)》1926,63(1641):586-587
929.
930.
Stahnke HL 《Science (New York, N.Y.)》1938,88(2277):166-167