全文获取类型
收费全文 | 6679篇 |
免费 | 385篇 |
国内免费 | 588篇 |
出版年
2024年 | 10篇 |
2023年 | 117篇 |
2022年 | 103篇 |
2021年 | 157篇 |
2020年 | 166篇 |
2019年 | 208篇 |
2018年 | 182篇 |
2017年 | 157篇 |
2016年 | 182篇 |
2015年 | 194篇 |
2014年 | 267篇 |
2013年 | 436篇 |
2012年 | 229篇 |
2011年 | 283篇 |
2010年 | 233篇 |
2009年 | 289篇 |
2008年 | 308篇 |
2007年 | 290篇 |
2006年 | 311篇 |
2005年 | 330篇 |
2004年 | 290篇 |
2003年 | 272篇 |
2002年 | 235篇 |
2001年 | 236篇 |
2000年 | 168篇 |
1999年 | 171篇 |
1998年 | 158篇 |
1997年 | 142篇 |
1996年 | 115篇 |
1995年 | 118篇 |
1994年 | 110篇 |
1993年 | 108篇 |
1992年 | 110篇 |
1991年 | 87篇 |
1990年 | 76篇 |
1989年 | 85篇 |
1988年 | 67篇 |
1987年 | 64篇 |
1986年 | 63篇 |
1985年 | 67篇 |
1984年 | 81篇 |
1983年 | 62篇 |
1982年 | 72篇 |
1981年 | 58篇 |
1980年 | 42篇 |
1979年 | 46篇 |
1978年 | 24篇 |
1977年 | 26篇 |
1976年 | 15篇 |
1973年 | 15篇 |
排序方式: 共有7652条查询结果,搜索用时 31 毫秒
31.
Experiments were conducted for 3 years at four locations and 1 year with six soil types at a common location in North Carolina to determine damage and control-cost functions for Heterodera glycines races 1 and 2 on soybean. In the experiments on native loamy sand and sandy soils, tolerance limits for initial population densities were 0 or very low, whereas in a muck, the tolerance limit was 315 eggs/500 cm³ soil. The aggressive race 2 was more damaging than race 1 in Lakeland sand and Norfolk loamy sand. The crop response was not different between races in the Appling sandy clay loam and Belhaven muck. Soybean yield responses to H. glycines were linear in six soil types in microplots at a common site. The amount of damage varied among these soil types, with lowest yields in the muck because of severe drought stress in this soil. An exponential function adequately described soybean yield response relative to nematode control with increasing rates of aldicarb in Norfolk loamy sand. Treatment with aldicarb in the Lakeland sand decreased the effective egg population of H. glycines but had only a minor effect in the muck. 相似文献
32.
Horst Grunz Thierry Darribère Jean -Claude Boucaut 《Development genes and evolution》1987,196(4):203-209
Summary Antibodies directed to fibronectin (anti-FN) were injected into the blastocoel of late blastulae of Xenopus laevis. Two animal caps (ectoderm) were isolated, when control embryos reached the early gastrula stage, and were combined with untreated upper blastopore lip in the sandwich method. In two control series fibronectin or Holtfreter solution was injected into the blastocoel. The results of the experiments suggest that neural induction cannot be prevented by binding anti-FN to fibronectin, which covers the blastocoelic side of the ectoderm. The data support the view that extracellular matrix proteins are not themselves responsible for neural induction. However, in comparison with the control series a slight shift of the differentiation pattern in the spinocaudal direction could be observed in the anti-FN series. The possible role of extracellular proteins in the formation of a close juxtaposition of mesodermal and ectodermal target cells as a prerequisite for shortdistance transmission of neural inducers is discussed. 相似文献
33.
The effects of various insecticides on the mycelial growth, sporulation and conidial germination of Metarhizium anisopliae var. anisopliae isolate E9 were studied in the laboratory. Chlorpyrifos was the most toxic organophosphate to mycelial growth and sporulation at all concentrations. Temephos, malathion and leptophos were highly toxic to sporulation while malathion was the most inhibitory to germination. The carbamates, carbofuran, methomyl and oxamyl were moderately toxic to mycelial growth and sporulation while oxamyl had an adverse effect on germination. The pyrethroids (pyrethrin, permethrin and resmethrin) and the insect growth regulators (diflubenzuron and methoprene) were not inhibitory to the various developmental stages of isolate E9. The chlorinated hydrocarbons (chlordane, lindane and toxaphene) were more deleterious than all other insecticide groups tested. Among the fungicides, benomyl and maneb produced the greatest inhibition. 相似文献
34.
本文首次报道柚花的香气成分。作者利用憎水性树脂XAD-4吸附柚鲜花的头香,并以毛细管气相色谱和毛细管气相色谱-质谱-计算机联用方法研究头香的化学组分,分离鉴定了17个已知化学成分。它们是芳樟醇、β-蒎烯、β-水芹烯、橙花叔醇等。 相似文献
35.
36.
37.
Theodor Günther Jürgen Vormann Jamaledin Ghaida 《Biological trace element research》1989,20(3):243-249
Application of salicylate increased the concentration of metallothionein (MT) in liver of pregnant rats as well as of adult male rats, whereas in fetal liver, MT was reduced by salicylate. Induction of MT synthesis by salicylate is an indirect effect because in cultured hepatocytes salicylate did not induce MT synthesis. Salicylate increased MT also in adrenalectomized rats. Indomethacin induced the same concentration of MT in maternal liver as salicylate. However, indomethacin had no effect on MT in fetal liver. Induction of MT in adult liver by salicylate and indomethacin was independent of zinc. 相似文献
38.
Karl H. Summer Dominik Klein Nada de Ruiter Josef Abel 《Biological trace element research》1989,21(1):165-169
In the present study we report on the effects of commonly used nonsteroidal antiinflammatory drugs on metallothionein (MT)
and MT-I mRNA levels. A single dose of chloroquine (100 mg/kg), diclofenac (100 mg/kg), indomethacin (10 mg/kg), or piroxicam
(100 mg/kg) was administered ip to C57B1 mice. After 18 h, MT levels were determined with a Cd-saturation radioassay. MT-I
mRNA levels were measured by Northern Blot analyses using a probe containing the mouse MT-I gene. All drugs tested caused
an increase in the MT content of the liver but not of the kidneys and lung. The lowest and highest effects were observed with
chloroquine (8 times the control value) and diclofenac (18 times), respectively. In accordance with the stimulation of MT
synthesis, increased accumulation of hepatic MT-I mRNA could be demonstrated.
These results indicate that elevated MT levels may contribute to the effectiveness of nonsteroidal antiinflammatory drugs
in the treatment of rheumatoid arthritis (RA). 相似文献
39.
A single intraperitoneal injection of DL-methionine (500 mg/kg body wt.) to adult male Wistar rats was shown to significantly
induce all the components of the hepatic microsomal mixed function oxidase system such as NADPH cytochrome C reductase activity,
cytochromes P-450 and b5, as well as activities of drug metabolizing enzymes such as aminopyrine demethylase and uridine 5′ -diphosphate-glucuronosyltransferase.
Combined administration of nicotinamide (250 mg/kg body wt.) and DL-methionine (500 mg/kg body wt.) was shown to bring about
an additional increase (25-30%) in the activities of these enzymes as compared to their induction on independent administration
of the two endobiotics. In rats bearing Yoshida sarcoma (ascites) tumour as well as in normal rats injected with serum from
tumour bearing animals, the decreased activities of hepatic mixed function oxidases could be restored to their normal levels
by administration of DL-methionine (500 mg/kg body wt.) to these rats. Whereas actinomycin D (1 mg/kg body wt.) had no effect
on the increased incorporation of [14C] labelled leucine into microsomal proteins following administration of nicotinamide, the enhanced incorporation of the label
following DL-methionine administration was completely inhibited by the same dose of actinomycin D. Administration of cycloheximide
(0·5 mg/kg body wt.) to rats could completely inhibit the increased incorporation of [14C] leucine into hepatic microsomal proteins following independent administration of nicotinamide and DL-methionine. Similar
inhibitory pattern with actinomycin D and cycloheximide was also demonstrated in case of induction of NADPH cytochromeC reductase activity by both these endobiotics. 相似文献
40.
Yuzuru Mikami Sen Feng Yu Katsukiyo Yazawa Kazutaka Fukushima Akio Maeda Jun Uno Kiyoshi Terao Naoki Saito Akinori Kubo Ken -ichiro Suzuki 《Mycopathologia》1990,112(2):113-118
During our studies on toxic substances from clinically isolated Nocarida, a new isolate identified as Nocardia otitidiscaviarum from cutaneous nocardiosis was found to produce a toxic substance called HS-6 that had strong in vitro as well as in vivo toxicity. The mouse intraperitoneal LD50 value was 1.25 mg/kg and the ED50 value for L1210 cultured cells was 0.3 ng/ml. The structure of HS-6 was determined and found to belong to the 16-membered macrocyclic group with a molecular formula of C43H68O12. HS-6 also showed activity against pathogenic fungi such as Cryptococcus neoformans. 相似文献