全文获取类型
收费全文 | 107667篇 |
免费 | 5570篇 |
国内免费 | 52篇 |
专业分类
林业 | 4481篇 |
农学 | 3145篇 |
基础科学 | 741篇 |
12171篇 | |
综合类 | 20807篇 |
农作物 | 4416篇 |
水产渔业 | 4958篇 |
畜牧兽医 | 55075篇 |
园艺 | 1245篇 |
植物保护 | 6250篇 |
出版年
2018年 | 1299篇 |
2017年 | 1426篇 |
2016年 | 1373篇 |
2015年 | 1151篇 |
2014年 | 1357篇 |
2013年 | 4062篇 |
2012年 | 2736篇 |
2011年 | 3354篇 |
2010年 | 2165篇 |
2009年 | 2153篇 |
2008年 | 3322篇 |
2007年 | 3048篇 |
2006年 | 2900篇 |
2005年 | 2726篇 |
2004年 | 2833篇 |
2003年 | 2759篇 |
2002年 | 2678篇 |
2001年 | 3285篇 |
2000年 | 3299篇 |
1999年 | 2448篇 |
1998年 | 1079篇 |
1997年 | 1088篇 |
1995年 | 1259篇 |
1994年 | 1168篇 |
1993年 | 1128篇 |
1992年 | 2367篇 |
1991年 | 2531篇 |
1990年 | 2440篇 |
1989年 | 2495篇 |
1988年 | 2274篇 |
1987年 | 2350篇 |
1986年 | 2486篇 |
1985年 | 2400篇 |
1984年 | 1920篇 |
1983年 | 1775篇 |
1982年 | 1166篇 |
1981年 | 1124篇 |
1980年 | 1029篇 |
1979年 | 1762篇 |
1978年 | 1425篇 |
1977年 | 1148篇 |
1976年 | 1133篇 |
1975年 | 1166篇 |
1974年 | 1524篇 |
1973年 | 1610篇 |
1972年 | 1585篇 |
1971年 | 1515篇 |
1970年 | 1408篇 |
1969年 | 1262篇 |
1967年 | 1094篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
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
63.
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
64.
Cellular alterations in level of expression of mRNA encoding for prostaglandin endoperoxide synthase were quantified within ovarian tissues of sheep obtained before, during and after induction of the preovulatory surge of LH and ovulation with LHRH. This was accomplished by isotopic in situ hybridization using a selective cRNA probe to ovine prostaglandin endoperoxide synthase mRNA. A significant elevation in mRNA was detected within the theca interna of the preovulatory follicle at 8, 16 and 24 hr following administration of LHRH. Very close to the time of ovulation (ie., at 24 hr post-LHRH) a marked rise in mRNA was observed in association with epithelial cells covering the apical surface of the follicle. Ovarian cyclooxygenase metabolites of arachidonic acid produced during the ovulatory process in the ewe originate within the thecal layer and germinal epithelium of the follicle destined to ovulate. 相似文献
65.
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
66.
67.
68.
69.
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
70.
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