全文获取类型
收费全文 | 28835篇 |
免费 | 3671篇 |
国内免费 | 2篇 |
出版年
2018年 | 287篇 |
2017年 | 258篇 |
2016年 | 474篇 |
2015年 | 751篇 |
2014年 | 832篇 |
2013年 | 1064篇 |
2012年 | 1295篇 |
2011年 | 1200篇 |
2010年 | 770篇 |
2009年 | 738篇 |
2008年 | 1100篇 |
2007年 | 1085篇 |
2006年 | 1003篇 |
2005年 | 966篇 |
2004年 | 946篇 |
2003年 | 948篇 |
2002年 | 916篇 |
2001年 | 916篇 |
2000年 | 911篇 |
1999年 | 767篇 |
1998年 | 395篇 |
1997年 | 368篇 |
1996年 | 347篇 |
1995年 | 320篇 |
1994年 | 321篇 |
1993年 | 334篇 |
1992年 | 681篇 |
1991年 | 628篇 |
1990年 | 611篇 |
1989年 | 660篇 |
1988年 | 561篇 |
1987年 | 601篇 |
1986年 | 475篇 |
1985年 | 564篇 |
1984年 | 479篇 |
1983年 | 385篇 |
1982年 | 398篇 |
1981年 | 358篇 |
1980年 | 328篇 |
1979年 | 435篇 |
1978年 | 382篇 |
1977年 | 336篇 |
1976年 | 313篇 |
1975年 | 334篇 |
1974年 | 381篇 |
1973年 | 361篇 |
1972年 | 305篇 |
1971年 | 285篇 |
1970年 | 247篇 |
1969年 | 246篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
5.
Sarah Easterby‐Smith 《Curtis's Botanical Magazine》2017,34(4):279-297
The correspondence exchanged between Captain John Blake, John Bradby Blake, and their associates offers a valuable insight into the sociable world of Enlightenment botany. By considering these sources alongside the records of other contemporary scholars of botany, this paper examines the composition of the community of plant collectors and botanical scholars with whom father and son were interacting in the 1760s and 1770s. The documents also reveal the ways in which botanical knowledge circulated among the members of these communities. Amateur botany, it turns out, was deeply linked to gardening and to the emerging trade in horticultural plants, yet the contributions made by gardeners and nurserymen have been largely overlooked. In sum, the Blake collection at Oak Spring helps to answer larger questions about the nature of Enlightenment sociability, about diversity within botanical networks, and about the ways in which that social diversity affected botanical collecting. 相似文献
6.
7.
A polymorphism was identified in the bovine butyrophilin (BTN) gene by digesting poly-merase chain reaction products with the restriction enzyme Hae III. This polymorphism was segregating in a Holstein-Friesian sire selected as part of an ongoing study directed towards the identification of quantitative trait loci affecting milk composition. Screening of a half-sib family established for the heterozygous sire allowed the localization of BTN to bovine chromosome 23 (BTA23). 相似文献
8.
9.
D H Broide C M Smith S I Wasserman 《Journal of immunology (Baltimore, Md. : 1950)》1990,145(6):1838-1844
As elevated bronchoalveolar lavage (BAL) fluid histamine levels are noted in patients with pulmonary fibrosis (PF), we assayed BAL fluid from 16 patients with PF for the presence of a histamine releasing factor (HRF). HRF activity was assayed by measuring release of the preformed mast cell-derived mediators, histamine, or beta-hexosaminidase (beta-hex) from a purified population of IL-3 dependent mouse bone marrow derived mast cells (MBMMC) or human blood basophils. Mean BAL cell free histamine levels in the patients with PF was 1226 +/- 1349 pg/ml, whereas BAL histamine levels in a comparison group of six non-PF patients was 118 +/- 60 pg/ml. HRF was significantly elevated in BAL fluid of patients with PF (mean beta-hex release 24.5 +/- 12.9%; range 6.8 to 52.4%) compared to the non-PF group of patients (mean beta-hex release 7.9 +/- 7.7%; range 1.8 to 20.7%). The PF HRF not only degranulated MBMMC, but also induced the generation of the arachidonic acid metabolite leukotriene C4 from MBMMC (24.6 +/- 4.2 ng leukotriene C4/10(6) MBMMC). The PF HRF did not appear to be a cytokine previously identified in BAL fluid of patients with PF (i.e., platelet derived growth factor or insulin growth factor-1) or a human cytokine able to degranulate human basophils (i.e., IL-1, or granulocyte-macrophage-CSF) as these recombinant human cytokines did not induce MBMMC beta-hex release. Physicochemical characterization of the HRF revealed that it was relatively heat stable, pronase sensitive and on Sephadex G-75 and G-200 column chromatography had an apparent molecular mass of 30 to 50 kDa. The ability of PF BAL to induce beta-hex release from MBMMC was not dependent on IgE as unsensitized or lactic acid treated MBMMC release similar amounts of beta-hex compared to MBMMC sensitized with IgE. Thus, BAL fluid of patients with PF contains an HRF that induces beta-hex release from MBMMC via an IgE-independent mechanism. The presence of the HRF could explain elevated BAL histamine levels in patients with PF. 相似文献
10.