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111.
High-resolution holocene environmental changes in the thar desert, northwestern india 总被引:2,自引:0,他引:2
Enzel Y Ely LL Mishra S Ramesh R Amit R Lazar B Rajaguru SN Baker VR Sandler A 《Science (New York, N.Y.)》1999,284(5411):125-128
Sediments from Lunkaransar dry lake in northwestern India reveal regional water table and lake level fluctuations over decades to centuries during the Holocene that are attributed to changes in the southwestern Indian monsoon rains. The lake levels were very shallow and fluctuated often in the early Holocene and then rose abruptly around 6300 carbon-14 years before the present (14C yr B.P.). The lake completely desiccated around 4800 (14)C yr B.P. The end of this 1500-year wet period coincided with a period of intense dune destabilization. The major Harrapan-Indus civilization began and flourished in this region 1000 years after desiccation of the lake during arid climate and was not synchronous with the lacustral phase. 相似文献
112.
Isolation, experimental transmission, and characterization of causative agent of Potomac horse fever 总被引:28,自引:0,他引:28
C J Holland M Ristic A I Cole P Johnson G Baker T Goetz 《Science (New York, N.Y.)》1985,227(4686):522-524
113.
Cruz-Migoni A Hautbergue GM Artymiuk PJ Baker PJ Bokori-Brown M Chang CT Dickman MJ Essex-Lopresti A Harding SV Mahadi NM Marshall LE Mobbs GW Mohamed R Nathan S Ngugi SA Ong C Ooi WF Partridge LJ Phillips HL Raih MF Ruzheinikov S Sarkar-Tyson M Sedelnikova SE Smither SJ Tan P Titball RW Wilson SA Rice DW 《Science (New York, N.Y.)》2011,334(6057):821-824
The structure of BPSL1549, a protein of unknown function from Burkholderia pseudomallei, reveals a similarity to Escherichia coli cytotoxic necrotizing factor 1. We found that BPSL1549 acted as a potent cytotoxin against eukaryotic cells and was lethal when administered to mice. Expression levels of bpsl1549 correlate with conditions expected to promote or suppress pathogenicity. BPSL1549 promotes deamidation of glutamine-339 of the translation initiation factor eIF4A, abolishing its helicase activity and inhibiting translation. We propose to name BPSL1549 Burkholderia lethal factor 1. 相似文献
114.
Trans-endocytosis of CD80 and CD86: a molecular basis for the cell-extrinsic function of CTLA-4 总被引:1,自引:0,他引:1
Qureshi OS Zheng Y Nakamura K Attridge K Manzotti C Schmidt EM Baker J Jeffery LE Kaur S Briggs Z Hou TZ Futter CE Anderson G Walker LS Sansom DM 《Science (New York, N.Y.)》2011,332(6029):600-603
Cytotoxic T lymphocyte antigen 4 (CTLA-4) is an essential negative regulator of T cell immune responses whose mechanism of action is the subject of debate. CTLA-4 shares two ligands (CD80 and CD86) with a stimulatory receptor, CD28. Here, we show that CTLA-4 can capture its ligands from opposing cells by a process of trans-endocytosis. After removal, these costimulatory ligands are degraded inside CTLA-4-expressing cells, resulting in impaired costimulation via CD28. Acquisition of CD86 from antigen-presenting cells is stimulated by T cell receptor engagement and observed in vitro and in vivo. These data reveal a mechanism of immune regulation in which CTLA-4 acts as an effector molecule to inhibit CD28 costimulation by the cell-extrinsic depletion of ligands, accounting for many of the known features of the CD28-CTLA-4 system. 相似文献
115.
Chromosome 17 deletions and p53 gene mutations in colorectal carcinomas 总被引:175,自引:0,他引:175
S J Baker E R Fearon J M Nigro S R Hamilton A C Preisinger J M Jessup P vanTuinen D H Ledbetter D F Barker Y Nakamura R White B Vogelstein 《Science (New York, N.Y.)》1989,244(4901):217-221
Previous studies have demonstrated that allelic deletions of the short arm of chromosome 17 occur in over 75% of colorectal carcinomas. Twenty chromosome 17p markers were used to localize the common region of deletion in these tumors to a region contained within bands 17p12 to 17p13.3. This region contains the gene for the transformation-associated protein p53. Southern and Northern blot hybridization experiments provided no evidence for gross alterations of the p53 gene or surrounding sequences. As a more rigorous test of the possibility that p53 was a target of the deletions, the p53 coding regions from two tumors were analyzed; these two tumors, like most colorectal carcinomas, had allelic deletions of chromosome 17p and expressed considerable amounts of p53 messenger RNA from the remaining allele. The remaining p53 allele was mutated in both tumors, with an alanine substituted for valine at codon 143 of one tumor and a histidine substituted for arginine at codon 175 of the second tumor. Both mutations occurred in a highly conserved region of the p53 gene that was previously found to be mutated in murine p53 oncogenes. The data suggest that p53 gene mutations may be involved in colorectal neoplasia, perhaps through inactivation of a tumor suppressor function of the wild-type p53 gene. 相似文献
116.
Baker CH 《Science (New York, N.Y.)》1963,141(3586):1196-1197
Short signals in a vigilance test generated an inferior initial performance, as compared with longer signals, and resulted in a steeper decrement in performance. A short (1-minute) and a long (2-hour) vigilance task was undertaken by each subject. 相似文献
117.
The paradox of keystone species persecuted as pests: A call for the conservation of abundant small mammals in their native range 总被引:1,自引:0,他引:1
Miguel Delibes-Mateos Andrew T. Smith Con N. Slobodchikoff Jon E. Swenson 《Biological conservation》2011,(5):1335-1346
Small mammals, such as European rabbits (Oryctolagus cuniculus), plateau pikas (Ochotona curzoniae) and prairie dogs (Cynomys spp.), traditionally have been perceived as pests and targeted for control within their native ranges, where they perform essential ecosystem roles and are considered keystone species. These species can reach high densities, and have been subjected to eradication campaigns because of their putative negative impact on natural habitats and agriculture and their competition with livestock for forage. Eradication programmes have been a main factor causing sharp declines of these species in their natural ranges. Paradoxically, they are keystone species where they are abundant enough to be perceived as pests. The term “pest” is usually a social perception that is rarely supported by scientific data, whereas there is considerable scientific evidence of the key ecological roles played by these species. We call for the conservation of these species and present a conceptual model regarding the management of their populations. Where they occur at high numbers, and hence their effects on biodiversity are still of crucial importance, the persecution of these species should be avoided and their natural habitats preserved. In areas with high conservation value, but where these species occur at low densities, management efforts should aim to increase their density. In areas of high commercial value, managers ideally should consider changing prioritization of the area to high conservation value by purchasing the land or obtaining conservation easements. In situations with high commercial value and demonstrable low conservation concern, small mammals could be reduced humanely. 相似文献
118.
A field experiment is described where three contrasting direct drilling coulters (seed groove openers) were used for a total of twelve drillings at fortnightyly intervals. Wheat was drilled into an undisturbed silt loam soil in a temperate climate during a spring-summer-autumn period in the southern hemisphere. An experimental chisel coulter promoted significantly larger counts of seedling emergence than a triple disc coulter in two of the drillings, and was also superior to a hoe coulter in one of the drillings. In very dry conditions, where in 3 weeks no seedling emergence occurred with any of the coulters, sub-surface seedlings in the grooves made by the chisel coulter had survived in a further two of the drillings than was the case with the triple disc and hoe coulters.These results confirmed that the biological effect of the coulters was largely a function of the physical geometry of the grooves which determined their ability to retain and utilize the liquid and vapour moisture present in the seed micro-environment. 相似文献
119.
120.
P. L. Brezonik L. A. Baker J. R. Eaton T. M. Frost P. Garrison T. K. Kratz J. J. Magnuson W. J. Rose B. K. Shephard W. A. Swenson C. J. Watras K. E. Webster 《Water, air, and soil pollution》1986,31(1-2):115-121
The controlled acidification of a two-basin lake is described. The lake was divided by a vinyl curtain in 1984; acidification of one basin began in 1985. Target pH values of 5.5, 5.0 and 4.5 are planned for 2-yr increments. Biotic and chemical responses and internal alkalinity generation are being studied. Baseline studies, initial results at pH 5.5, and predictions of lake responses to acidification are described. 相似文献