全文获取类型
收费全文 | 105784篇 |
免费 | 5450篇 |
国内免费 | 52篇 |
专业分类
林业 | 4319篇 |
农学 | 3044篇 |
基础科学 | 731篇 |
11708篇 | |
综合类 | 20782篇 |
农作物 | 4298篇 |
水产渔业 | 4633篇 |
畜牧兽医 | 54451篇 |
园艺 | 1199篇 |
植物保护 | 6121篇 |
出版年
2018年 | 1205篇 |
2017年 | 1335篇 |
2016年 | 1286篇 |
2015年 | 1092篇 |
2014年 | 1263篇 |
2013年 | 3937篇 |
2012年 | 2577篇 |
2011年 | 3195篇 |
2010年 | 2080篇 |
2009年 | 2060篇 |
2008年 | 3211篇 |
2007年 | 2945篇 |
2006年 | 2811篇 |
2005年 | 2645篇 |
2004年 | 2753篇 |
2003年 | 2685篇 |
2002年 | 2628篇 |
2001年 | 3277篇 |
2000年 | 3293篇 |
1999年 | 2449篇 |
1998年 | 1076篇 |
1997年 | 1085篇 |
1995年 | 1256篇 |
1994年 | 1167篇 |
1993年 | 1122篇 |
1992年 | 2369篇 |
1991年 | 2537篇 |
1990年 | 2440篇 |
1989年 | 2499篇 |
1988年 | 2280篇 |
1987年 | 2355篇 |
1986年 | 2490篇 |
1985年 | 2398篇 |
1984年 | 1921篇 |
1983年 | 1777篇 |
1982年 | 1165篇 |
1981年 | 1123篇 |
1980年 | 1028篇 |
1979年 | 1762篇 |
1978年 | 1425篇 |
1977年 | 1148篇 |
1976年 | 1132篇 |
1975年 | 1165篇 |
1974年 | 1526篇 |
1973年 | 1615篇 |
1972年 | 1586篇 |
1971年 | 1518篇 |
1970年 | 1412篇 |
1969年 | 1263篇 |
1967年 | 1097篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
142.
Thomasson JR 《Science (New York, N.Y.)》1978,199(4332):975-977
Morphological study of fossil grass anthoecia of Berriochloa and Nassella collected from Miocene-Pliocene strata in Kansas has revealed well-preserved epidermal structure. This seems to be the first micromorphological information known from fossil grass floral bracts. The epidermal pattern on the lemma in the fossils and their living counterparts are evidence in support of the view that the North American species of Stipa of the section Hesperostipa Elias and species of Piptochaetium have a common ancestry in Berriochloa, and that species of both taxa have been distinct from species of the Nassella, Oryzopsis, and other Stipa since at least the Miocene or Pliocene. 相似文献
143.
R Boyne 《Research in veterinary science》1978,24(2):134-138
The cytochrome oxidase activity of circulating leucocytes was investigated by means of a semiquantitative method using blood films. A significant decrease in activity was found in male rats, cattle and sheep that had been deprived of copper. During copper depletion, leucocyte cytochrome oxidase activity declined more slowly than did plasma copper concentration and plasma ferroxidase I activity, and so was less sensitive as a guide to the copper status of the animal. 相似文献
144.
P. VIDHYASEKARAN R. RABINDRAN M. MUTHAMILAN K. NAYAR K. RAJAPPAN N. SUBRAMANIAN & K. VASUMATHI 《Plant pathology》1997,46(3):291-297
Pseudomonas fluorescens strain Pf1, inhibitory to the growth of the rice blast pathogen Pyricularia oryzae in vitro , was developed as a talc-based powder formulation. When rice seeds were treated with this formulation, the bacteria spread to roots, stems and leaves of the plants and protected against leaf infection by P. oryzae . When applied as a foliar spray, the bacteria survived on the leaves. The powder formulation controlled leaf blast under greenhouse conditions. In tests as a seed treatment and foliar spray in four field trials it effectively controlled the disease and increased grain yield. 相似文献
145.
Modelling crop:weed interactions in wheat with ALMANAC 总被引:1,自引:0,他引:1
ALMANAC is a dynamic model for plant growth, water balance and soil nitrogen dynamics that can simulate on a daily basis two or more competing species. The simulation of competition for light is based on Beer's law, allowing a different extinction coefficient ( k ) for each species. Light is partitioned between species based on k -values, leaf area index and plant heights. Total hiomass is simulated with radiation use efficiency and grain yield with a harvest index approach, sensitive to water stress. The model simulates competition for water and nutrients based on each species current rooting zone and demand by each species. The effect of crop management on the competition issue can he simulated. The model was evaluated in Dijon (France) using 4 years of experimental data on wheat:oat mixtures, differing in oat ( Avena sativa L.) densities, the period of oat emergence, the date of weed suppression by herbicides and the wheat ( Triticun aestivum L.) genotype. Additional data on oilseed rape ( Brassica nupus L.) and vetch ( Vilcia sauiva L.) competition in spring wheat were also used. The wheat grain yield was reasonably simulated with a root mean square error (RMSE) of 0.10-0.35 t ha-1 . Corresponding values for oats were 0.10-0.55 t ha-1 . The competitiveness of oats, oilseed rape and vetch was correctly simulated. The model appears as a reasonable tool for estimating damage thresholds in integrated weed control programmes. 相似文献
146.
M. Szydlowski M. Stachowiak M. Mackowski M. Kamyczek R. Eckert M. Rozycki M. Switonski 《Zeitschrift für Tierzüchtung und Züchtungsbiologie》2004,121(3):149-155
Porcine leptin gene (LEP) and its association with production traits was analysed in the Polish Large White (PLW, n = 135), Polish Landrace (PL, n = 120) and synthetic line 990 (L990, n = 184). Two fragments of exon 3 of LEP were studied with the use of RFLP and SSCP techniques. The frequencies of C allele for the T3469C polymorphic site were 0.11, 0.10 and 0.11 in PLW, PL and L990, respectively. Phenotypic data were collected for the average daily weight gain, the feed conversion ratio, the weight of abdominal fat, backfat thickness (five measurements), intramuscular fat, meat content, loin weight, loin muscle area, ham weight and ham cut weight. The contrasts between TT and TC genotypes at the T3469C polymorphic site were estimated in the unitrait Animal Model with genotype at the RYR1 locus included. The lowest p values occurred for association test between T3469C polymorphism and intramuscular fat content in PLW (0.26 ± 0.14%, p = 0.05) and loin weight in L990 (?0.32 ± 0.13 kg, p = 0.01). We conclude that the detected associations are population‐specific and the analysed polymorphism of the LEP gene does not contribute directly to genetic variability of growth and carcass traits in pigs. 相似文献
147.
Ken R. Ito Tomonori Sato Hiro Goto Katsuyoshi Sato Jun Watanabe Masaki Yokoo 《The Journal of Poultry Science》2022,59(3):247
Increasing food loss and waste (FLW) is a global problem, and efforts are being made to use waste food as potential livestock feed material. The amount of self-supplied feed is lower in Japan than in other countries, and the government recommends FLW use for animal feed. Sake (Japanese rice wine) is a traditional alcoholic beverage. During the sake manufacturing process, large amounts of squeezed solids or “lees” (sake lees) are generated. Sake lees are nutritious and functional, but are prone to spoilage. In this study, we investigated whether sake lees should be mixed with animal feed immediately or after drying. To assess the usefulness of sake lees as a poultry feed ingredient and determine the effect of sake lees on intestinal immunity, we performed a feeding trial with three treatments: a raw sake lees (RSL) diet, dried sake lees (DSL) diet, and control diet. Three-week-old broilers were fed these diets (n=8 per group) for two weeks. We then calculated feed efficiency and performed RT-qPCR to assess the effects of diet on intestinal immunity. The growth performance in the RSL diet group was equivalent to that in the control diet group. The DSL diet became difficult for broilers to eat, resulting in decreased growth performance. In the ileum of RSL-diet broilers, the mRNA expression levels of TGF-β1 and avian β-defensin (AvBD)12 were significantly increased compared to those of control diet broilers (p<0.05), and a significant correlation was observed between the two genes (p<0.05). Our results indicated that sake lees should not be dried and should be mixed immediately with feed, and this sake lees when fed to chicken activates the intestinal immunity. However, sake lees have a lower fat content than corn, and it is thus important to combine sake lees with high-energy feed. 相似文献
148.
A proton magnetic resonance spectroscopic method for determining disulfiram in the bulk drug product and in the formulated material was collaboratively studied. The method depends on the use of chloroform-d as a solvent and hexamethylcyclotrisiloxane as the internal standard. No interference from tablet excipients was observed. The method is rapid and specific. Eighteen laboratories analyzed duplicate samples of a bulk drug product, a 250 mg tablet composite, and a 500 mg tablet composite. The average per cent results and standard deviations were 99.7 +/- 1.4, 100.9 +/- 2.0, and 99.9 +/- 2.2, respectively. 相似文献
149.
150.
Little information exists concerning the effects of long-term fungicide programs on the qualitative and quantitative characteristics of fusaria in turfgrasses and in turfgrass soils. These effects were studied on Poa pratensis L, turfgrasses at three locations, using 14 fungicides, one nematicide, and five mixed fungicide programs. Some fungicides increased the numbers of fusaria in soil and thatch, some had no effect, and others greatly reduced the numbers. Changes in Fusarium species' compositions occurred independently from the changes in propagule numbers. The proportion of Fusarium-colonized turfgrass crowns was generally higher in fungicide-treated than in nontreated turfgrasses. 相似文献