全文获取类型
收费全文 | 6978篇 |
免费 | 1088篇 |
国内免费 | 3746篇 |
出版年
2024年 | 93篇 |
2023年 | 257篇 |
2022年 | 365篇 |
2021年 | 417篇 |
2020年 | 416篇 |
2019年 | 452篇 |
2018年 | 276篇 |
2017年 | 293篇 |
2016年 | 300篇 |
2015年 | 430篇 |
2014年 | 628篇 |
2013年 | 541篇 |
2012年 | 738篇 |
2011年 | 671篇 |
2010年 | 587篇 |
2009年 | 594篇 |
2008年 | 637篇 |
2007年 | 620篇 |
2006年 | 542篇 |
2005年 | 475篇 |
2004年 | 359篇 |
2003年 | 313篇 |
2002年 | 241篇 |
2001年 | 252篇 |
2000年 | 248篇 |
1999年 | 162篇 |
1998年 | 100篇 |
1997年 | 74篇 |
1996年 | 42篇 |
1995年 | 46篇 |
1994年 | 26篇 |
1993年 | 23篇 |
1992年 | 27篇 |
1991年 | 39篇 |
1990年 | 38篇 |
1989年 | 38篇 |
1988年 | 24篇 |
1987年 | 21篇 |
1986年 | 31篇 |
1985年 | 19篇 |
1984年 | 17篇 |
1983年 | 20篇 |
1982年 | 31篇 |
1981年 | 17篇 |
1980年 | 13篇 |
1979年 | 11篇 |
1978年 | 10篇 |
1975年 | 19篇 |
1965年 | 12篇 |
1964年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
Joe T. Ritchie 《Plant and Soil》1981,58(1-3):81-96
2.
3.
4.
Bell , C. Ritchie (U. of North Carolina, Chapel Hill.), and Lincoln Constance . Chromosome Numbers in Umbelliferae. II. Amer. Jour. Bot. 47(1) : 24-32. Illus. 1960.–Chromosome numbers are reported for plants representing an additional 100 taxa of Umbelliferae. Chromosome numbers for 77 of these taxa are published here for the first time, previously published chromosome numbers of 19 taxa are verified, and numbers differing from those previously published are reported in 4 instances. Ten of the genera included here have been previously unknown cytologically. Polyploidy has been discovered in Bowlesia and confirmed in Pimpinella. Aneuploid series appear to occur in Eremocharis, Eryngium, Oenanthe, Perideridia, and Ptilimnium. Every chromosome count is referable to a cited herbarium specimen. 相似文献
5.
6.
急性脑梗死约占全部脑卒中的70%,病死率和致残率高,且极易复发。但目前针对急性脑梗死在时间窗内溶栓、抗凝等治疗手段不能从根本上切实有效地修复受损脑组织,且伴有出血等风险。寻找脑梗死形成发展的原因并予以治疗迫在眉睫。酸中毒是引起缺血性脑损伤的重要机制。大量实验研究表明,酸中毒能加重神经元的缺血性损伤,且其梗死面积与酸中毒的程度直接相关。但缺血产生的酸中毒如何引起神经元损伤的确切机制尚不明确。最近研究发现酸中毒能激活一种在中枢及周围神经中广泛存在的膜通道,即酸敏感离子通道,它对Ca2+通透,能引起细胞内Ca2+超载,同时能激活胞内酶引起细胞内蛋白质、脂类及核酸的降解,加重缺血后脑损伤。本文就酸敏感离子通道1a与脑梗死做一综述。 相似文献
7.
A synthesis of adenosine-5′-d (4), and its p.m.r. spectral characteristics, are described. The presence of deuterium in 4 gives rise to a 2:1 mixture of R and S configurations at C-5, thereby permitting specific assignments for the resonances of the residual 5′-protons. From the observed spin-spin coupling between the latter and H-4′, and estimate has been made of the rotamer population of the exocyclic 5′-carbinol group. It is shown that the gauche-gauche rotamer is preponderant (≈70%) and the gauche-trans one of minor importance (≈20%) in aqueous solution, which contrasts markedly with the preference for the latter rotamer exhibited by adenosine in the solid state. 相似文献
8.
Peter J. Syapin Terry Ritchie Lorna Noble Ernest P. Noble 《Journal of neurochemistry》1987,48(4):1285-1290
The relationship between the stability of potential neurochemical markers and autolysis time was studied at 4 degrees C and 25 degrees C using postmortem brain samples from two rat strains. In general, qualitatively similar results were obtained with either N/Nih or Sprague-Dawley rats; however, quantitative differences were often observed, particularly in regard to benzodiazepine receptor changes. For every enzyme activity or binding property examined, no significant change was found when brains were kept at 4 degrees C for up to 72 h prior to freezing at -70 degrees C. Na,K-ATPase and low-affinity Ca-ATPase activities were also stable in brains kept at 25 degrees C for up to 72 h. Mg-ATPase activity was reduced in brains kept at 25 degrees C for 24 and 48 h. [3H]Guanidinoethylmercaptosuccinic acid [( 3H]GEMSA) binding to enkephalin convertase in the cytosol was not significantly changed in brains kept at 25 degrees C; however, a small increase was seen for [3H]GEMSA binding to the membrane fraction at 24, but not 48 and 72 h postmortem. [3H]Quinuclidinyl benzilate [( 3H]QNB) binding to muscarinic cholinergic receptors decreased in brains kept at 25 degrees C for 72 h. Opioid receptor binding also decreased in brains kept at 25 degrees C. Using [3H]2-D-alanine-5-D-leucine enkephalin to label delta opioid receptors, a statistically significant decrease in binding was observed as early as 6 h postmortem, and was completely abolished after 72 h at 25 degrees C. In contrast, [3H]naloxone binding was unchanged after 24 h at 25 degrees C, but was decreased after 48 and 72 h.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
9.
黑龙江省三江平原丹顶鹤的数量分布 总被引:2,自引:0,他引:2
在地面调查的基础上,我们使用Y-11轻型飞机对黑龙江省三江平原地区的丹顶鹤的数量分布近行了调查,调查时飞行高度80米,航速140公里/小时,续航里程共3748公里。调查结果表明,丹顶鹤在三江平原主要分布在8个地区,其中嘟噜河下游、洪河自然保护区、七星河流域和兴凯湖低地是主要繁殖地,总数量共309只。 相似文献
10.
在整理青海省蚤类标本中,发现长刺双蚤 Amphipsylla longispina Scalon, 1950一新亚种,记述如下。 长刺双蚤共和亚种 Amphipsylla longis pina gongheensis新亚种 鉴别特征 新亚种可动突前缘较直,不动突较细长,阳茎钩突端部似鸟头状; 相似文献