全文获取类型
收费全文 | 256986篇 |
免费 | 14703篇 |
国内免费 | 670篇 |
专业分类
林业 | 23523篇 |
农学 | 13969篇 |
基础科学 | 2950篇 |
42663篇 | |
综合类 | 26717篇 |
农作物 | 17259篇 |
水产渔业 | 16877篇 |
畜牧兽医 | 98571篇 |
园艺 | 6291篇 |
植物保护 | 23539篇 |
出版年
2021年 | 2467篇 |
2020年 | 2851篇 |
2019年 | 3626篇 |
2018年 | 3972篇 |
2017年 | 4299篇 |
2016年 | 4725篇 |
2015年 | 4290篇 |
2014年 | 5664篇 |
2013年 | 16224篇 |
2012年 | 5982篇 |
2011年 | 7865篇 |
2010年 | 7295篇 |
2009年 | 7859篇 |
2008年 | 7282篇 |
2007年 | 6376篇 |
2006年 | 6990篇 |
2005年 | 6191篇 |
2004年 | 6105篇 |
2003年 | 5873篇 |
2002年 | 5248篇 |
2001年 | 5846篇 |
2000年 | 5569篇 |
1999年 | 5290篇 |
1998年 | 4127篇 |
1997年 | 4206篇 |
1996年 | 3883篇 |
1995年 | 4475篇 |
1994年 | 3861篇 |
1993年 | 3563篇 |
1992年 | 4256篇 |
1991年 | 4461篇 |
1990年 | 4236篇 |
1989年 | 4235篇 |
1988年 | 3793篇 |
1987年 | 3822篇 |
1986年 | 3703篇 |
1985年 | 4018篇 |
1984年 | 3700篇 |
1983年 | 3556篇 |
1982年 | 2915篇 |
1981年 | 2817篇 |
1980年 | 2777篇 |
1979年 | 3371篇 |
1978年 | 2939篇 |
1977年 | 2752篇 |
1976年 | 2565篇 |
1974年 | 2790篇 |
1973年 | 2766篇 |
1972年 | 2597篇 |
1971年 | 2531篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
In field experiments methabenzthiazuron at 1.1 kg ai/ha applied pre-emergence gave good control of Poa trivialis L. in perennial ryegrass S23 which was undersown in spring barley (Zephyr); no significant damage to barley or perennial ryegrass resulted from 2.2 kg ai/ha. However this dose applied when barley had three to four leaves decreased the subsequent barley yield. In pot experiments in the glasshouse methabenzthiazuron was active mainly due to uptake through the soil. Much greater damage to barley and perennial ryegrass resulted when herbicide-treated soil was placed below seed level than above the seed. The difference was less marked with P. trivialis. The latter started to develop secondary roots near the soil surface earlier than either perennial ryegrass or spring barley. 相似文献
992.
H T?nhardt J Dorst B Schülke H Sajonski 《Archiv fuer experimentelle veterinaermedizin》1976,30(5):733-738
Testicular tissue and blood samples (V. spermatica interna) were taken from 32 boars during castration. The animals were different age groups. Against this background, studies were conducted into the correlations between testicular and plasma testosterone, on the one hand, and the amount of interstitial cells of Leydig in testicular tissue as well as the latters' cell nuclei volumes, on the other. The results seemed to support the conclusion that any age-dependent increase of testicular and plasma testosterone concentrations was caused unambigously by an absolute increase in volume of androgenic testicular tissue, in concomitance with testicular growth, in other words, by rise in the total number of interstitial cells of Leydig. 相似文献
993.
Fifty six 1,2,3-benzothiadiazoles and related compounds were evaluated as carbaryl synergists against the house fly (Musca domestica). Many of these were excellent synergists, the most active being those containing various combinations of halogen, alkyl, or alkoxy substituents in the 5- and/or 6-positions of the ring.Regression analysis on the data from 14 compounds for which substituents constants were available established that synergistic activity can be satisfactorily described by equations in terms of the hydrophobic bonding constant (π) and the homolytic free radical constant (σ ·).The results with compounds related to the 1,2,3-benzothiadiazoles suggest that synergistic activity is associated primarily with the diazosulfide moiety. 相似文献
994.
The interaction of phosphine with purified cytochrome c and cytochrome oxidase was studied by absorption and circular dichroic spectrometry. Treatment of cytochrome oxidase with phosphine yielded absorption spectra in both the visible and Soret region that were similar to that produced by dithionite. Striking changes in the circular dichroic spectra were also recorded, sugesting that a valence change of the heme iron was accompanied by a conformation change of the prosthetic group.Phosphine treatment of cytochrome c also yielded spectra similar to those produced by reduction with dithionite suggesting a valence change of the heme iron. However, both the time necessary for complete reduction and the concentration of phosphine necessary for this effect suggest that, in comparison with cytochrome oxidase, cytochrome c was relatively insensitive. Reduction of cytochrome oxidase by phosphine had only a very minor effect on the intrinsic dichroic spectrum suggesting little effect on the polypeptide chains.The persistence of a component after reduction by phosphine and the subsequent reduction of this component by dithionite suggests that phosphine primarily reduced only one comonent of the cytochrome aa3 complex. The failure of EDTA and fluoride, which are known ligands of cytochrome a3 to affect the reduction of cytochrome aa3 by phosphine, as well as the occurrence of a 436-nm isosbestic point of the ferric-ferrous absorption spectra suggests that phosphine reduced primarily cytochrome a. However, it is argued that a slow reduction of cytochrome a3 cannot be ruled out. 相似文献
995.
Methomyl {S-methyl-N-[(methylcarbamoyl)oxy]thioacetimidate}, also known as Lannate, may exist in two geometric configurations but the more stable syn isomer is the form applied as an insecticide. In the rat, syn[14CN]methomyl [CH3S(CH3)CNOC(O)NHCH3] was metabolized to respiratory 14CO2 and in a ratio of about 2 to 1. Studies with the anti isomer showed that it was metabolized predominately to . These and other data are presented supporting the contention that syn methomyl is partially isomerized to the anti isomer in the animal prior to the hydrolysis of the ester linkage. After hydrolysis, the syn oxime [CH3S(CH3)14CNOH] is further metabolized to 14CO2 while the anti oxime is metabolized to . Proposed immediate precursors to the carbon dioxide and acetonitrile, formed by Beckmann rearrangement of the syn and anti oximes, are CH3S14C(O)NHCH3 and , respectively. 相似文献
996.
Through the use of a critical electrolyte concentration staining technique, the glycosaminoglycans (GAGs) in the nucleus pulposus region of the canine intervertebral disc were arbitrarily identified as "hyaluronic acid", chondroitin sulphate and keratan sulphate. Approximate estimates of GAG concentration could be qualitatively deduced by determining the appropriate GAG "ALCIANOPHILIC INDEX". This index was considered to be an effective qualitative adjunct to chemical quantitation of GAGs in the intervertebral disc. 相似文献
997.
998.
999.
T.A. Miller 《Pesticide biochemistry and physiology》1976,6(4):307-319
Three criteria, latency to convulsions, still period, and recovery are used to distinguish between carbamate and phosphate insecticide poisoning in house flies, Musca domestica. Because of shorter latencies with carbamate-treated flies, the central nervous system was considered more sensitive to the presence of carbamates than phosphates. Recovery from carbamate-induced tetany was considered correlated with reactivation of carbamylated cholinesterase. There appeared to be a fundamental difference between the insecticidal actions of carbamates and phosphates not wholly explainable by cholinesterase inhibition. Tethered or held house flies were less susceptible to poisoning than unrestrained flies. 相似文献
1000.
The spectral interactions of 45 insecticide synergists and related compounds with oxidized and reduced cytochrome P-450 from microsomes of insecticide-resistant and -susceptible house flies were investigated. The type III interaction typical of piperonyl butoxide was the most common spectral interaction for the compounds studied. In addition to this, several other varients of the type III interaction were noted. In general these responses with house fly microsomes were similar to those reported for mammals, although some minor species and strain differences were observed. The cytochrome P-450 from susceptible house flies, although reported previously not to exhibit type I difference spectra with many xenobiotics, was found to elicit this spectral response with several methylenedioxyphenyl compounds. 相似文献