全文获取类型
收费全文 | 131500篇 |
免费 | 11065篇 |
国内免费 | 4646篇 |
专业分类
147211篇 |
出版年
2025年 | 96篇 |
2024年 | 1447篇 |
2023年 | 1700篇 |
2022年 | 3484篇 |
2021年 | 5781篇 |
2020年 | 4203篇 |
2019年 | 5001篇 |
2018年 | 4672篇 |
2017年 | 3490篇 |
2016年 | 4954篇 |
2015年 | 7110篇 |
2014年 | 8368篇 |
2013年 | 8901篇 |
2012年 | 10630篇 |
2011年 | 9718篇 |
2010年 | 6007篇 |
2009年 | 5423篇 |
2008年 | 6254篇 |
2007年 | 5678篇 |
2006年 | 4995篇 |
2005年 | 3990篇 |
2004年 | 3424篇 |
2003年 | 3175篇 |
2002年 | 2708篇 |
2001年 | 3863篇 |
2000年 | 3585篇 |
1999年 | 3005篇 |
1998年 | 1426篇 |
1997年 | 1421篇 |
1996年 | 1284篇 |
1995年 | 1145篇 |
1994年 | 1029篇 |
1993年 | 819篇 |
1992年 | 1474篇 |
1991年 | 1155篇 |
1990年 | 920篇 |
1989年 | 796篇 |
1988年 | 635篇 |
1987年 | 567篇 |
1986年 | 426篇 |
1985年 | 415篇 |
1984年 | 238篇 |
1983年 | 222篇 |
1982年 | 138篇 |
1981年 | 126篇 |
1980年 | 87篇 |
1979年 | 107篇 |
1977年 | 82篇 |
1974年 | 76篇 |
1973年 | 86篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
Abstract: The leaf extracts of Populus nigra were collected and identified by steam distillation, air entrainment and gas chromatographic–mass spectrometric analysis. Electroantennograms were recorded from Helicoverpa armigera adults in response to the chemicals identified. Both aromatic compounds and green-leaf volatiles elicited strong responses. Field experiments revealed that the active compounds responsible for attracting H. armigera moths are mainly short-side-chain aromatic alcohols and aldehydes. We, for the first time, used agaropectin as the controlled-release matrix of insect attractants. A five-component lure containing all the aromatics without phenolics, mixed in the proportions as found in the steam distillate of the leaves collected in August, produced the best trap catch. The results showed that the volatiles of wilted leaves of P. nigra can attract H. armigera adults by feeding attraction. 相似文献
3.
Xue-Yuan Dong Yun-Yan Li Xiao-Ang Yang Wei-Feng Chen 《Biochimie et biologie cellulaire》2004,82(5):577-582
In an effort to identify novel Cancer-Testis genes, we analyzed the sequence in the q26-28 region of human X chromosome by several on-line tools. The candidate sequences were then confirmed by experiments. We have obtained a novel Cancer-Testis gene, BJ-HCC-20. In vivo, it was found to have two isoforms. In samples of liver, colon, gastric and lung cancer tested, the expression frequency of BJ-HCC-20 is 25%, 17%, 21% and 15%, respectively. Full-length cDNAs of both BJ-HCC-20 isoforms were isolated and their gene structures and promoter regions were characterized. BJ-HCC-20 might have implications in theoretical and practical tumor biology. 相似文献
4.
本文就植物血细胞凝集素(PHA)作用的不同时间对小鼠脾脏淋巴细胞γ-谷氨酰基转肽酶(γ-GT)活性的影响进行了观察。结果表明,脾脏淋巴细胞转化率随给予PHA时间的延长而上升,对照组<24h组<48h组<72h组;淋巴细胞γ-GT活性于24h明显强于对照组(P<0.001),随着PHA作用时间的延长其γ-GT活性逐渐下降,即48h组与对照组已无显著差异,而72h组却低于对照组(P<0.001)。可见PHA在小鼠体内对γ-GT活性有很大影响。 相似文献
5.
应用纤维连接素(Fn)、S—100蛋白、胶质纤维酸性蛋白(GFAP)、细胞角蛋白(CK)和神经特异性烯醇蛋白(NSE)5种抗体对63例正常人垂体前叶内滤泡星状细胞(FSC)进行了免疫细胞化学研究。结果表明:人FSC内26.9%S_(100)阳性,9.3%GFAP阳性,63.8%两者都为阳性。CK、NSE和Fn均为阳性。从而提示了FSC来自神经外胚层的原始细胞而非Rathke's囊上皮的残留。 相似文献
6.
本文主要阐述了一种具有纤溶活性的枯草杆菌(Bacillussubtilis)蛋白激酶产生菌株的筛选与鉴定的研究结果。作者从初筛的12株Bacillussublilis菌中,通过对固体发酵和液体发酵所产生的枯草杆菌蛋白激酶,用琼脂糖-纤维蛋白平板法测其活性,经比较不同菌株的活性,筛选出两株高产酶菌株:B.subtilisHW—12和B.subtilisHW—3。同时对菌体和菌落形态特点、生理生化反应进行了鉴定,认为B.SubtilisHW-12菌株可用来做为发酵生产该酶的菌种。 相似文献
7.
W. L. Li P. D. Chen L. L. Qi D. J. Liu 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1995,90(3-4):526-533
A species-specific repeated sequence, pHvNAU62, was cloned from Haynaldia villosa, a wheat relative of great importance. It strongly hybridized to H. villosa, but not to wheat. In situ hybridization localized this sequence to six of seven H. villosa chromosome pairs in telomeric or sub-telomeric regions. Southern hybridization to whea-H. villosa addition lines showed that chromosomes 1V through 6V gave strong signals in ladders while chromosome 7V escaped detection. In addition to H. villosa, several Triticeae species were identified for a high abundance of the pHvNAU62 repeated sequence, among which Thinopyrum bassarabicum and Leymus racemosus produced the strongest signals. Sequence analysis indicated that the cloned fragment was 292 bp long, being AT rich (61%), and showed 67% homology of pSc7235, a rye repeated sequence. Isochizomer analysis suggested that the present repeated sequence was heavily methylated at the cytosine of the CpG dimer in the genome of H. villosa.It was also demonstrated that pHvNAU62 is useful in tagging the introduced 6VS chromosome arm, which confers a resistance gene to wheat powdery mildew, in the segregating generations. 相似文献
8.
9.
The effects on the fecundity and fertility of redbanded leafroller, Argyrotaenia velutinana (Walker), and obliquebanded leafroller,Choristoneura rosaceana (Harris), exposed as adults to surfaces treated with the ecdysone agonists tebufenozide (RH-5992) and methoxyfenozide (RH-2485) were examined. The first part of the study consisted of recently emerged moths being exposed to treated surfaces continuously throughout their lives (including mating and oviposition). Continuous exposure to tebufenozide- or methoxyfenozide-treated surfaces significantly reduced the mean number of eggs laid and the percent of eggs that hatched in both species. The second part of the study involved exposure of recently emerged virgin moths (by sex) to treated surfaces for 24 h, after which, the exposed moths were paired with a nontreated partner to mate and oviposit on nontreated surfaces. In this experiment, for A. velutinana, significant reductions in fecundity occurred only when the female was exposed to methoxyfenozide-treated surfaces. Significant reductions in A. velutinana egg fertility occurred with both male and female exposure in the methoxyfenozide treatments and only female exposure in the tebufenozide treatments. For C. rosaceana, significant reductions in fecundity occurred with both male and female exposure in the tebufenozide and methoxyfenozide treatments. Significant reductions in C. rosaceana egg fertility occurred with both male and female exposure in the tebufenozide treatments and only with female exposure in the methoxyfenozide treatments. 相似文献
10.
X. Pochon L. Garcia-Cuetos A. C. Baker E. Castella J. Pawlowski 《Coral reefs (Online)》2007,26(4):867-882
Recent molecular studies of symbiotic dinoflagellates (genus Symbiodinium) from a wide array of invertebrate hosts have revealed exceptional fine-scale symbiont diversity whose distribution among
hosts, regions and environments exhibits significant biogeographic, ecological and evolutionary patterns. Here, similar molecular
approaches using the internal transcribed spacer-2 (ITS-2) region were applied to investigate cryptic diversity in Symbiodinium inhabiting soritid foraminifera. Approximately 1,000 soritid specimens were collected and examined during a 12-month period
over a 40 m depth gradient from a single reef in Guam, Micronesia. Out of 61 ITS-2 types distinguished, 46 were novel. Most
types found are specific for soritid hosts, except for three types (C1, C15 and C19) that are common in metazoan hosts. The
distribution of these symbionts was compared with the phylotype of their foraminiferal hosts, based on soritid small subunit
ribosomal DNA sequences, and three new phylotypes of soritid hosts were identified based on these sequences. Phylogenetic
analyses of 645 host-symbiont pairings revealed that most Symbiodinium types associated specifically with a particular foraminiferal host genus or species, and that the genetic diversity of these
symbiont types was positively correlated with the genetic diversity found within each of the three host genera. Compared to
previous molecular studies of Symbiodinium from other locations worldwide, the diversity reported here is exceptional and suggests that Micronesian coral reefs are
home to a remarkably large Symbiodinium assemblage. 相似文献