全文获取类型
收费全文 | 4845篇 |
免费 | 261篇 |
国内免费 | 361篇 |
出版年
2023年 | 47篇 |
2022年 | 80篇 |
2021年 | 90篇 |
2020年 | 125篇 |
2019年 | 146篇 |
2018年 | 140篇 |
2017年 | 153篇 |
2016年 | 181篇 |
2015年 | 162篇 |
2014年 | 233篇 |
2013年 | 340篇 |
2012年 | 146篇 |
2011年 | 265篇 |
2010年 | 195篇 |
2009年 | 322篇 |
2008年 | 360篇 |
2007年 | 303篇 |
2006年 | 273篇 |
2005年 | 223篇 |
2004年 | 192篇 |
2003年 | 202篇 |
2002年 | 137篇 |
2001年 | 93篇 |
2000年 | 99篇 |
1999年 | 109篇 |
1998年 | 80篇 |
1997年 | 70篇 |
1996年 | 82篇 |
1995年 | 56篇 |
1994年 | 39篇 |
1993年 | 55篇 |
1992年 | 43篇 |
1991年 | 40篇 |
1990年 | 35篇 |
1989年 | 27篇 |
1988年 | 26篇 |
1987年 | 28篇 |
1986年 | 13篇 |
1985年 | 22篇 |
1984年 | 23篇 |
1983年 | 18篇 |
1982年 | 33篇 |
1981年 | 24篇 |
1980年 | 30篇 |
1979年 | 24篇 |
1978年 | 17篇 |
1977年 | 11篇 |
1976年 | 14篇 |
1975年 | 9篇 |
1973年 | 21篇 |
排序方式: 共有5467条查询结果,搜索用时 26 毫秒
81.
A. Torres-Barragán E. Zavaleta-Mejía Carmen González-Chávez Ronald Ferrera-Cerrato 《Mycorrhiza》1996,6(4):253-257
A field experiment was carried out to determine the effects of the inoculation of onion (Allium cepa L.) with Glomus sp. Zac-19 on the development of onion white rot (Sclerotium cepivorum Berk.) and on onion production. Mycorrhization delayed onion white rot epidemics by 2 weeks and provided a significant protection
against the disease for 11 weeks after onion transplanting, as compared with nonmycorrhizal controls. Mycorrhizal plants showed
an increase of 22% in yield, regardless of the presence of the white rot pathogen.
Accepted: 8 January 1996 相似文献
82.
被囊动物中生物活性物质研究的一些进展 总被引:1,自引:0,他引:1
本文对近年从海鞘中提取分离的环肽类及生物碱类化合物作了综述,对一些典型化合物如Didemnins、Patellamides、Merdine、Eudistomins及Ecteinascidins等作了较详细的介绍。 相似文献
83.
生物制品检定动态管理系统的开发和应用 总被引:1,自引:0,他引:1
掌握生物制品的检定动态是质量管理的重要内容,由于检定周期随着制品种类、批数及检定条件的变化而变化,以往靠手工方式查阅繁杂的检定记录,难以随时快速、全面了解当时的检定状况。检定动态管理软件的开发可应用计算机自动跟踪显示检定进度和检定状态,及时反映制品质量和检定条件变化,明显提高了生产和质量管理部门的工作效率。 相似文献
84.
Alternaria infectoria E . G . Simmons was isolated from naturally infected eggs of the fig wax scale insect , Ceroplastes rusci L . (Homoptera: Coccidae) , that were showing different degrees of shriveling . This fungus proved to be pathogenic to eggs , nymphs and adults of this pest . The fungus had significant effects on both the mortality and hatchability of the eggs ( P = 0 . 0001) . Three days after exposure to the fungus , nearly one - third (31 . 5%) of the fungus - treated eggs became discolored and 17% showed moderate shrinking but no mortality . Fifteen days post - application , 91% of the fungus - treated eggs were diseased (74 . 8% of them were dead) due to A. infectoria, while no disease developed on the untreated eggs . Hatching decreased by 39 . 6% over a 15 - day period in the fungus - treated eggs compared to the control . Additionally , crawlers hatching from fungus - treated eggs became infected . The fungus seemed to induce crawlers to enter the settling stage . Seventy - two per cent of the fungus - treated crawlers versus 9% of the untreated controls entered the settling stage 6 days after exposure to the fungal inoculum . The highest level of nymphal mortality attributed to A. infectoria occurred when 30% (wet w:v blended mycelium in water containing 0 . 5% w:v Metamucil) inoculum was applied , and a high relative humidity was maintained for the following 48 h . This is the first record of A. infectoria on the fig wax scale and for the genus Alternaria as an entomopatho genic fungus . 相似文献
85.
Aspects of the biology and host range of Sibinia fastigiata Clark (Coleoptera: Curculionidae) were studied to assess its safety for release in Australia as a biological control agent of the weed Mimosa pigra L . (Mimosaceae) . Larvae feed on the seeds and adults on open flowers of their host . Adults oviposit on to immature seeds 3 mm long or less and hence seeds of this length and maturity were used in the host range tests and for rearing . Females are shown to avoid previously attacked seeds enhancing their effectiveness as seed destroyers . Survival of adults was higher when provided with open flowers . The host range was determined using laboratory control - choice oviposition tests on excised plant material and , in the field in the native range , no - choice oviposition tests on living plants , surveys of adults on plants , and breeding of insects from pods of plants of various legume species . The control - choice oviposition tests employed a new design in which the control plant alone was offered to the insects followed by a choice of test plants species . Other than M. pigra, only one plant species was acceptable for oviposition , the closely related M. asperata. Larval development also occurs on M. asperata and this host is occasionally used in the field . This insect was approved for release in March 1997 . 相似文献
86.
D. M. Kolodny-Hirsch T. Sitchawat T. Jansiri A. Chenrchaivachirakul U. Ketunuti 《Biocontrol Science and Technology》1997,7(4):475-488
Small - scale field trials were conducted in the Kanchanaburi and Ratchaburi provinces of Thailand between December 1994 and March 1996 to gather efficacy data to support a registration dossier for a commercial formulation of a nuclear polyhedrois virus of beet armyworm , Spodoptera exigua, under the tradename Spod - X . A liquid concentrate formula tion of Spod - X was compared with two commercial standards , Bacillus thuringiensis subsp . aizawai (CenTuri 3 . 5 WDG) and the insect growth regulator tebufenozide (Mimic 20F , a benzoylhydrazine ecdysone agonist) , for control of beet armyworm on garden pea , Chinese kale , shallot and table grape . Spod - X applied at 4 - day intervals at 3 . 1 - 12 . 5 1011 occlusion bodies (OBs) ha 1 in a spray volume of 625 - 1000 l ha 1 provided excellent control of beet armyworm on garden pea and grape (75 - 100 % reductions) after the second application . On Chinese kale and shallot , rates of Spod - X in the rate 5 - 60 1011 OBs ha 1 sprayed every 4 days in a spray volume of 1000 l ha 1 provided significant protection from infestation of beet armyworm over the growing season; however , efficacy was poor to moderate . Tank - mixing Spod - X with the pyrethroid , deltamethrin (Decis3EC) , did not improveefficacy on shallot;however , combinations of virus and B. thuringiensis or tebufenozide achieved commercially acceptable levels of crop protection on Chinese kale compared with virus alone . Lower levels of control and crop pro tection observed with all materials on Chinese kale and shallot reflect , in part , the tendency of S. exigua larvae to feed within sheltered sites and directly damage marketable plant parts . In general , all rates of Spod - X performed as well as , or better than , the B. thuringiensis standard (56 . 3 - 105 g ha 1 a.i.) on all crops tested . In general , reductions of beet armyworm larval populations and plant damage provided by all labeled rates of the chemical standard , tebufenozide (125 - 250 g ha 1 a . i .), were marginally greater than all rates of Spod - X tested . On crops such as pea and grape , where beet armyworm predominately feed on exposed leaf surfaces , our data unequivocally support the use of Spod - X for cost - effective , season - long pest management . Strategies to improve the efficacy of virus on shallot and kale are discussed . 相似文献
87.
Donatella Marazziti Lionella Palego Chiara Mazzanti Stefano Silvestri Giovanni B. Cassano 《Chronobiology international》1995,12(2):100-105
Our study aimed to investigate the possible presence of seasonal changes in platelet phenolsulfotransferase (ST) in a group of 20 healthy, drug-free subjects of both sexes and between 24 and 37 years of age. Blood samples were taken four times a year in the period immediately following the equinoxes and the solstices. The results showed that both STs underwent seasonal changes: the lowest values were found in autumn and in winter, and the highest in the summer. A positive correlation between the two STs and the length of the photoperiod was observed in winter, whereas in the spring we detected a negative correlation between the TL ST and the photoperiod length. Future studies should clarify whether platelet ST of patients with mood disorders shows a similar seasonality. 相似文献
88.
The distribution of Rastrococcus invadens among different host plants and the impact of the mealybug on mango growth were investigated on 2067 trees in three surveys across all the ecological zones of Benin. The first survey started in 1989, less than 1 year after the first release of the exotic parasitoid Gyranusoidea tebygi. Within 3 years, G. tebygi had colonized the entire area of infestation, and was found on practically all infested mango trees as well as other infested host plants. By 1991, the incidence of R. invadens on the secondary host plants had declined significantly. The percentage of infested mango trees declined from 31.0% in 1989 to 17.5% in 1991, highest populations being found in the coastal savanna. During the same period, the mean percentage of infested mango trees having indigenous predators declined from 42.3 to 20.9%. Average mealybug densities declined steadily from 9.7 females/48 leaves in 1989, with 3.2% of all mango trees having densities above 100 mealybugs, to 6.4 females/48 leaves in 1991, with 1.3% of all trees having densities above 100 mealybugs. In multiple regression analyses, based on 23 meteorological, agronomic and plant variables, the duration of the parasitoid's presence proved to be a major factor. It influenced mealybug population densities and sooty mould incidence, which, in turn, affected the production of new leaves. In all analyses, the impact of rainfall, for example, on the sooty mould or the mealybug was less important than the effect of G. tebygi. The present study demonstrates for the first time on a large scale the impact of G. tebygi on R. invadens and, indirectly, on its main host plant, mango. 相似文献
89.
Under controlled conditions, application of Steinernema carpocapsae using a baiting method consistently reduced the oviposition of Listronotus oregonensis adults at all moisture regimens. At 80 and 95% relative humidity, soil applications at 10 4 infective juveniles (IJs) cm-2 and 10 5 infective stages (400 IJs cm-2) per pot reduced the survival and oviposition of L. oregonensis adults; soil applications were ineffective at relative humidity lower than 80%. When timed correctly, soil application at the rate of 2 105 IJs/linear meter of row (4.4 109 IJs ha-1) reduced damage by up to 59%. 相似文献
90.
Conserving biological diversity requires a major effort in conducting survey and inventories, establishing priorities, selecting protected areas, managing resources and monitoring the effects of management. Systematics has an important contribution to make to each of these five major activities. Further, the new Convention on Biological Diversity requires systematics information to support action under virtually all of its substantive conservation and sustainable use articles. It seems apparent that large reference collections contribute directly to development, and development assistance agencies should recognize that investing in maintaining these collections is a legitimate form of development assistance. 相似文献