全文获取类型
收费全文 | 150070篇 |
免费 | 8770篇 |
国内免费 | 806篇 |
专业分类
林业 | 5614篇 |
农学 | 4701篇 |
基础科学 | 1110篇 |
17756篇 | |
综合类 | 29689篇 |
农作物 | 5885篇 |
水产渔业 | 7092篇 |
畜牧兽医 | 76493篇 |
园艺 | 2016篇 |
植物保护 | 9290篇 |
出版年
2019年 | 1570篇 |
2018年 | 2165篇 |
2017年 | 2507篇 |
2016年 | 2309篇 |
2015年 | 2136篇 |
2014年 | 2468篇 |
2013年 | 5692篇 |
2012年 | 4703篇 |
2011年 | 5630篇 |
2010年 | 3768篇 |
2009年 | 3611篇 |
2008年 | 5195篇 |
2007年 | 5073篇 |
2006年 | 4694篇 |
2005年 | 4459篇 |
2004年 | 4081篇 |
2003年 | 4166篇 |
2002年 | 3921篇 |
2001年 | 4627篇 |
2000年 | 4523篇 |
1999年 | 3604篇 |
1998年 | 1566篇 |
1997年 | 1422篇 |
1996年 | 1298篇 |
1995年 | 1515篇 |
1994年 | 1401篇 |
1993年 | 1372篇 |
1992年 | 2914篇 |
1991年 | 3125篇 |
1990年 | 2972篇 |
1989年 | 2974篇 |
1988年 | 2723篇 |
1987年 | 2848篇 |
1986年 | 2979篇 |
1985年 | 2732篇 |
1984年 | 2263篇 |
1983年 | 1997篇 |
1982年 | 1381篇 |
1979年 | 1957篇 |
1978年 | 1585篇 |
1977年 | 1339篇 |
1976年 | 1322篇 |
1975年 | 1414篇 |
1974年 | 1820篇 |
1973年 | 1807篇 |
1972年 | 1756篇 |
1971年 | 1659篇 |
1970年 | 1571篇 |
1969年 | 1460篇 |
1967年 | 1279篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
CERES-Maize (Vl. 0) predicted no grain yield when 100% defoliation occurred during vegetative growth. This result conflicted with field observations where 100% defoliation early in the vegetative stage did not materially reduce grain yield. CERES-Maize was modified to realistically predict yields when defoliation greater than 50% occurred during vegetative growth by taking into account stem (stem proper and sheath) photosynthesis and translocation of dry matter from the stem to the developing leaves. With these modifications, predictions from CERES-Maize were in good agreement with field measurements when defoliation occurred both early and later in the vegetative stage. This modified version of CERES-Maize can be the basis of a decision support system for defoliating pests of corn where yields can be evaluated under different management strategies and climate scenarios. 相似文献
72.
C M Honnas 《Veterinary Clinics of North America: Equine Practice》1991,7(3):695-722
Several surgical conditions affecting the foot can be successfully managed with the horse standing. Many factors affect the clinician's choice of whether to perform surgery with the horse standing or anesthetized. Temperament or pregnancy of the horse and economics may influence the decision to perform surgery with the horse standing. This article discusses several foot conditions that can be treated successfully in the ambulatory horse. 相似文献
73.
For practical reasons, a large volume (i.e. 5 ml) of frozen boar semen per insemination dose is desirable, but successful freezing has not been achieved, since optimal cooling rates have not yet been established. Post-thaw motility and the acrosome intep'ty of semen from four boars frozen with a programmable freezin machine, in mini-(0.25 ml), maxi-(5 ml) plastic straws and in 10 × 5 cm PVC- or Teflon FEP-plastic bags (0.35 – 0.12 mm thick, 5 ml) was studied. The freezing of the semen was monitored using thermocouples placed in the straws and the bags. The freezing curve started from +5°C, at a rate of −3°C/min, to – 6°C, it was held for 1 min at −6°C, and was followed by further drop to −100°C at a rate of −20°C/min, with subsequent storage in LN2 . The bags had a much shorter freezing point plnteau, compared to the maxi-straws. Post-thaw sperm motility was significantly higher when semen was frozen in mini-straws or in bags than in maxi-straws. The freezing procedure did not cause major acrosomal damages, significantly more normal apical ridges being present in the bags and mini-straws than in the maxi-straws. This in vitro evaluation indicates that the freezing method employed is satisfactory for freezing large volumes of boar semen into plastic bags . 相似文献
74.
Individual antigens of goats 总被引:1,自引:0,他引:1
75.
As anaerobic sampling and culture techniques improved, the documented prevalence of anaerobic bacteria in periodontal disease has increased. The anaerobic bacteria have become more well-known in humans and consequently in dogs, since this species is a major model in periodontal studies. A review of the literature related to anaerobic flora is described. 相似文献
76.
RNA was extracted from single or small groups of ovine ovarian follicles after treatment of ewes with FSH and/or LH. The content of mRNA for the alpha-inhibin and beta A-inhibin subunits was analyzed by hybridization with specific cDNA probes. All ewes were treated with progestin vaginal pessaries to suppress spontaneous preovulatory follicle maturation and ewes were given three intramuscular injections of gonadotropins at 8-hr intervals starting 24 hr prior to collection of ovaries. In experiment I, both Schering-FSH and NIDDK-oFSH-17 (oFSH) significantly increased alpha- and beta A-inhibin mRNA per ewe in 2-5 mm follicles and tended to increase alpha- and beta A-inhibin mRNA in large (greater than 5 mm) follicles. In experiment II, oFSH and NIDDK-oLH-25 (oLH) were administered in a 2X2 factorial arrangement. Separate administration of oFSH or oLH increased (P less than .05) the alpha-inhibin mRNA concentration in large follicles. alpha-inhibin mRNA concentration in 4-5 mm follicles was also increased by oFSH but was decreased by oLH. Concomitant treatment with oFSH and oLH did not change alpha-inhibin mRNA concentrations from those measured in oFSH treated ewes. In experiment II, beta A mRNA concentrations followed a pattern similar to that of alpha A mRNA, but the differences were not statistically significant. We conclude that, in the ewe, exogenous FSH increases the concentration of inhibin mRNA in the whole follicle. The ability of exogenous oLH to alter expression of the inhibin subunit genes may depend upon the stage of follicle maturation. 相似文献
77.
L A Janssens 《Veterinary surgery : VS》1991,20(4):274-278
Seven foci of pain (trigger points) were identified in the triceps brachii, infraspinatus, adductor-pectineus, peroneus longus, gluteus medius, ileocostorum lumborum, and quadriceps femoris muscles in 48 lame dogs. The dogs had been lame for 1 day to 150 weeks (mean, 24 weeks). Thirty-one dogs had been treated unsuccessfully with corticosteroids, nonsteroidal anti-inflammatory drugs, analgesics, or acupuncture. Palpating the trigger points induced severe pain. Treatment consisted of weekly stimulation of the trigger points by needling or injection of a local anesthetic. The mean treatment period was 2.8 weeks. Excellent results and complete recovery were observed in 34 dogs (60%). 相似文献
78.
R. Iori O. Leoni L. Lazzeri G. Mosca S. Palmieri 《Journal of Agronomy and Crop Science》1991,167(2):91-95
Samples of rapeseed from three Italian growing environments (Bologna, Perugia and Palermo) were analysed for glucose content and dry weight of 1000 seeds every three or four days starting from the end of flowering until complete ripening. In addition, the content of oil, soluble and total proteins, glucosinolates and myrosinase activity was determined in samples of mature seeds. The cultivars used were jet Neuf and Lingot (type 0) and Tandem, Jade and Santana (type 00). From the results it emerged that the point of intersection of the two branches of the linear regression plots for different glucose-consumption kinetics found during seed filling, in addition to being strongly affected by the climate of the test environment, is correlated with quantitative and qualitative production, independently of the genotype. 相似文献
79.
80.