全文获取类型
收费全文 | 100524篇 |
免费 | 5424篇 |
国内免费 | 4304篇 |
专业分类
林业 | 7452篇 |
农学 | 8045篇 |
基础科学 | 3557篇 |
13308篇 | |
综合类 | 21829篇 |
农作物 | 4640篇 |
水产渔业 | 4439篇 |
畜牧兽医 | 38190篇 |
园艺 | 2144篇 |
植物保护 | 6648篇 |
出版年
2022年 | 1222篇 |
2021年 | 1942篇 |
2020年 | 1760篇 |
2019年 | 1925篇 |
2018年 | 1847篇 |
2017年 | 2196篇 |
2016年 | 2043篇 |
2015年 | 2484篇 |
2014年 | 2412篇 |
2013年 | 4631篇 |
2012年 | 3972篇 |
2011年 | 4543篇 |
2010年 | 3630篇 |
2009年 | 3613篇 |
2008年 | 4079篇 |
2007年 | 4141篇 |
2006年 | 3797篇 |
2005年 | 3691篇 |
2004年 | 2471篇 |
2003年 | 2386篇 |
2002年 | 2179篇 |
2001年 | 2593篇 |
2000年 | 2687篇 |
1999年 | 2744篇 |
1998年 | 1699篇 |
1997年 | 1534篇 |
1996年 | 1440篇 |
1995年 | 1430篇 |
1994年 | 1336篇 |
1993年 | 1293篇 |
1992年 | 1802篇 |
1991年 | 1886篇 |
1990年 | 1678篇 |
1989年 | 1618篇 |
1988年 | 1430篇 |
1987年 | 1302篇 |
1986年 | 1325篇 |
1985年 | 1272篇 |
1984年 | 1008篇 |
1983年 | 941篇 |
1979年 | 915篇 |
1978年 | 712篇 |
1976年 | 715篇 |
1975年 | 721篇 |
1974年 | 869篇 |
1973年 | 846篇 |
1972年 | 820篇 |
1971年 | 730篇 |
1970年 | 774篇 |
1969年 | 736篇 |
排序方式: 共有10000条查询结果,搜索用时 192 毫秒
41.
42.
43.
本文介绍了以一缩二乙二醇丙烯酸双酯(简称一缩双酯,DEGDA)和丙烯酸β-羟丙酯(简称羟丙酯,HPA)为单体,以N,N-二甲基苯胺/糖精为促进剂/助促进剂或仅用三氯乙酸作促进剂来配制厌氧胶粘剂(厌氧胶)的优化配方试验.所得厌氧胶综合性能良好,通过优化试验结果得知的规律性认识有一定意义. 相似文献
44.
45.
Jennifer B. Grimm DVM MS Kurt A. Grimm DVM MS Stephen K. Kneller DVM MS William J. Tranquilli DVM MS Sonia S. Crochik DVM MS Matthew G. Bischoff DVM Jennifer L. Podolski DVM 《Veterinary radiology & ultrasound》2001,42(5):458-462
The effects of intramuscularly administered medetomidine and butorphanol (MB), and medetomidine, butorphanol, atropine (MBA) on glomerular filtration rate (GFR) were determined in six dogs as measured by 99m-Tc-labeled diethylenetriaminepentaacetic acid (99mTc-DTPA) nuclear scintigraphy. Direct systolic, diastolic, and mean arterial blood pressures and heart rate were measured at regular time intervals before, during, and after GFR calculations. The mean GFR measurement following MB was significantly greater (4.44 ml/min/kg) than following MBA (3.82 ml/min/kg) or saline treatment (3.41 ml/min/kg). There was no significant difference between the mean GFR measurements following MBA injection and following saline injection. Diastolic and mean arterial pressures following MBA injection were significantly higher than the values recorded after either MB or saline alone. Heart rate following MB administration was significantly lower than that recorded for dogs receiving MBA or saline alone. The results of this study indicate that the administration of medetomidine in combination with butorphanol significantly increases total GFR in healthy dogs, while the administration of the combination of medetomidine, butorphanol, and atropine does not. 相似文献
46.
Abstract – The reproductive biology of three species of rainbowfish (Melanotaeniidae) in northeastern Australian rainforest streams was investigated. Two species, Melanotaenia eachamensis and Cairnsichthys rhombosomoides are endemic to the area, whereas the third, M. splendida splendida, is more widespread. The species were all highly fecund, producing many hundreds of eggs between 1.10 and 1.24 mm in diameter. Melanotaenia eachamensis was the most fecund, produced the largest eggs of the three species, and consequently exhibited the greatest maternal investment (as measured by gonadosomatic index). The majority of reproductive effort occurred during the dry season, although reproductively active fish were present year-round for each of the species, but particularly so for M. s. splendida and C. rhombosomoides. No evidence for a role by temperature or photoperiod as environmental cues for reproduction was found, and it was suggested that gonad development was strongly tied to somatic growth. The concentration of reproduction to the dry season ensures that larvae are produced during a period of relatively stable and benign physical conditions. Comparison of temporal changes in gonadosomatic index values suggest that the spawning season of M. eachamensis , which occurs in high-elevation streams, is more restricted and commences about 1 month earlier than either other species. A similar phenology was observed for the M. s. splendida population found at high elevation and highlights the potential for spatial differences in stream productivity to influence life history. Note 相似文献
47.
选取 1998年若干衡量企业技术开发活动投入与产出水平方面的指标进行计算 ,通过与全国大中型工业企业对比分析 ,揭示林业大中型工业企业存在的差距 ,为林业工业企业和有关部门采取相应措施以改变其落后状况提供参考。 相似文献
48.
W W Chan K Y Chen H Liu L S Wu J H Lin 《The Journal of veterinary medical science / the Japanese Society of Veterinary Science》2001,63(10):1057-1062
Since the International Society of Veterinary Acupuncture (IVAS) was founded in 1974, acupuncture (AP) has received greater acceptance by veterinary professionals throughout the world. This article introduces some important animal diseases that respond well to AP therapy. These include resuscitation of small animals, treatment of anoestrous gilts and sows, bovine reproductive disease, canine vertebral problems and equine backpain, etc. Conventional medicine considers these to be difficult cases to treat. Veterinarians have become more aware of the benefits of AP especially for those diseases, thanks to the efforts of experienced practitioners and scientists, and the many published reports on veterinary AP that have introduced some good indications for AP therapy in veterinary practice. Possible mechanisms behind the effectiveness of AP are discussed. This article aims to introduce veterinarians to good indications for AP to initiate their interest in the practice of AP. Although this is a rapidly expanding field, a long march must begin with one step. We wish this article to be the shoes for such a march. For more information on veterinary AP, contact IVAS , P.O. Box 1478, Longmont, CO.. 80502, USA (http://www.ivas.org), or your national veterinary acupuncture society (http://www.komvet.at/ ivadkom/vapsocs.htm). 相似文献
49.
鸡的微卫星DNA标记与胴体性状的相关分析 总被引:4,自引:1,他引:3
测定了青脚麻鸡与隐性白鸡杂交后自交的F2代个体的全净堂重、全净堂率、脂肪宽带、腹脂重和腹脂率6个胴体性状,检测10个微卫星DNA标记,对标记基因型胴体性状值进行方差分析和多重比较,结果表明:MCW328对于10周龄体重和全净膛重两性状各基因型均有显著的差异(P<0.05);ADL292对于腹脂重性状各基因型有极显著的差异(P<0.01),对于腹脂率有显著的差异(P<0.05)。MCW328标记基因与控制10周龄体重和全净膛重QTL连锁,ADL292标记基因与控制腹脂重和腹脂率QTL连锁。 相似文献
50.
B. Götz 《Journal of pest science》1938,14(8):92-93
Ohne Zusammenfassung 相似文献