全文获取类型
收费全文 | 4142篇 |
免费 | 298篇 |
国内免费 | 265篇 |
出版年
2023年 | 82篇 |
2022年 | 66篇 |
2021年 | 122篇 |
2020年 | 128篇 |
2019年 | 161篇 |
2018年 | 132篇 |
2017年 | 173篇 |
2016年 | 164篇 |
2015年 | 127篇 |
2014年 | 170篇 |
2013年 | 351篇 |
2012年 | 160篇 |
2011年 | 232篇 |
2010年 | 149篇 |
2009年 | 197篇 |
2008年 | 208篇 |
2007年 | 234篇 |
2006年 | 194篇 |
2005年 | 185篇 |
2004年 | 122篇 |
2003年 | 115篇 |
2002年 | 125篇 |
2001年 | 98篇 |
2000年 | 85篇 |
1999年 | 72篇 |
1998年 | 66篇 |
1997年 | 62篇 |
1996年 | 54篇 |
1995年 | 52篇 |
1994年 | 46篇 |
1993年 | 40篇 |
1992年 | 49篇 |
1991年 | 43篇 |
1990年 | 38篇 |
1989年 | 29篇 |
1988年 | 23篇 |
1987年 | 20篇 |
1986年 | 25篇 |
1985年 | 28篇 |
1984年 | 38篇 |
1982年 | 20篇 |
1981年 | 28篇 |
1980年 | 28篇 |
1979年 | 29篇 |
1978年 | 19篇 |
1977年 | 18篇 |
1976年 | 16篇 |
1975年 | 19篇 |
1974年 | 20篇 |
1973年 | 19篇 |
排序方式: 共有4705条查询结果,搜索用时 15 毫秒
101.
三种桉叶油化学成分研究 总被引:11,自引:0,他引:11
通过水蒸汽蒸油试验,发现已贮藏半年多的风干桉叶,仍有较高的含油量。云南省弥勒产的直杆桉(Eucalyptus maidenii)得油率为4.14%,蓝桉(E.globulus)为3.5%,福建省惠安产的窿缘桉(E.exserta)为1.2%,桉叶油生产厂也可以通过贮藏的风干桉叶生产桉叶油。通过气相色谱和质谱分析,从直杆桉叶油中鉴定出44个组份,蓝桉叶油中鉴定出35个组份,窿缘桉叶油中鉴定出26个组份。三种桉叶油单萜部分的组份基本一致,只是相对含量各有不同。桉油素含量,以直杆桉最高为68.02%,其次是蓝桉为67.54%,窿缘桉最低为34.33%。直杆桉、蓝桉可以怍材、油两用树种,窿缘桉不宜作油用树种。 相似文献
102.
103.
印楝油对褐稻虱雌虫求偶鸣声和交尾行为的影响 总被引:3,自引:0,他引:3
笔者用印楝(Azadirachta indica A. Juss)油点滴褐稻虱[Nilaparvata lugens(stal)]初羽化雌虫背部,点滴量分别为1.0、2.5及5.0μg,或将试虫饲养在分别用3%、6%及9%印楝油乳液喷雾处理过的稻株上.结果表明印楝油对褐稻虱雌虫正常的发声和交尾行为有明显干扰.8.3—25.0%的处理雌虫不能发声,也不交尾;8.3—58.3%发出不正常的求偶鸣声;其余鸣声虽基本正常,但脉冲重复频率增高,鸣叫持续时间缩短.后者可完成交尾,交尾前历时明显延长,但交尾时间与对照无显著差异. 相似文献
104.
FRANCOISE GUERRINI CENDRINE SEGUR DIDIER GARGANI MICHEL TIBAYRENC MICHEL DOLLET 《The Journal of eukaryotic microbiology》1992,39(4):516-521
ABSTRACT We studied 31 Phytomonas stocks isolated from various hosts and a broad geographical range by isoenzyme electrophoresis (14 loci) and population genetics analysis. The total variability is considerable since many stocks share no allele. Population genetic analysis strongly suggests that Phytomonas zymodemes behave as natural clones, as already proposed by us for several other protozoan species. These clones should be considered as actual taxa in all applied studies. Latex plants and phloemic plants (coconut and palm trees) harbor distinct sets of clones; hence, latex plants studied in this article are probably not a reservoir for parasites of the coconut and palm tree. 相似文献
105.
The cytotoxic and mutagenic effect of (±)-7β,8α-dihydroxy-9α,10α-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (anti BPDE) in normally excision diploid human cells treated just prior to onset of S was compared with that of cells allowed ~ 16 h for excision repair before onset of S and with that observed in excision-deficient serodema pigmentosum (SP12BE) cells. The cells were synchronized by release from density inhibition of cell replication. DNA synthesis began ~ 22 h after the cells were plated at lower density (i.e., 1.4 × 104 cells/cm2). The frequency of thioguanine-resistant mutants induced in normal cells treated just prior to onset of S was ~ 12- to 16-fold higher than that observed in cells treated in early G1 or treated in G0 (confluence) and then plated at lower density. The frequency approximated that expected for XP12BE cells from extrapolation of data obtained at lower doses. The frequency of mutants measured in normal cells treated in exponential growth was also much higher than that in the cells treated in early G1 or in G0, No such difference could be seen in XP12BE cells treated in exponential growth or in G0. In contrast to the mutagenicity data in the normal cells, there was no significant difference in the slope of the survival curve of normal cells treated at various times prior to S phase at low densities. However, normal cells treated even at the onset of S exhibited survival equal to XP12BE cells give a 4- to 5-fold lower dose. The data support the hypothesis that DNA synthesis is the cellular event which converts unexcised DNA lesions into mutations. However, they indicate that S is not the event primarily responsible for translating DNA damage into cell death. Accompanying studies on the rate of excision of anti BPDE adducts from the normal cells during the period priot to S support the conclusions. 相似文献
106.
Aqueous extracts of Ocimum sanctum and O. basilicum leaves contained compounds that killed Meloidogyne incognita larvae in 160 min. Thin layer and gas-liquid chromatography, and infrared spectrophotometry indicated that the essential oils eugenol and linalool were the active nematicidal compounds. 相似文献
107.
Twenty-seven mainly terpenoid constituents were identified in the essential oil of Mikania micrantha whole plant. Higher terpenoids present in the same plant included two kaurene derivatives and taraxasterol. 相似文献
108.
Louis Piovetti Christian Francisco Ginette Pauly Otmane Benchabane Colette Bernard-Dagan Anne Diara 《Phytochemistry》1981,20(6):1299-1302
Analysis of wood essential oil of Cupressus dupreziana revealed 26 components: 13 monoterpenes and 13 sesquiterpenes. The main components were carv 相似文献
109.
The monoterpenes of the fruits of Pittosporum resiniferum and P. undulatum have been identified. The essential oil of P. resiniferum contai 相似文献
110.
The trunk wood of Ocotea cymbarum from the Amazon basin contains α-phellandrene, α-pinene, eugenol, dehydrodieugenol and its monomethyl ether, as well as the previously unknown dehydrodieugenol-B (4,5′-diallyl-2′-hydroxy-2,3′-dimethoxydiphenyl ether). 相似文献