全文获取类型
收费全文 | 19454篇 |
免费 | 1435篇 |
国内免费 | 1346篇 |
专业分类
22235篇 |
出版年
2024年 | 52篇 |
2023年 | 292篇 |
2022年 | 633篇 |
2021年 | 1069篇 |
2020年 | 710篇 |
2019年 | 893篇 |
2018年 | 805篇 |
2017年 | 616篇 |
2016年 | 882篇 |
2015年 | 1255篇 |
2014年 | 1474篇 |
2013年 | 1511篇 |
2012年 | 1757篇 |
2011年 | 1537篇 |
2010年 | 952篇 |
2009年 | 815篇 |
2008年 | 945篇 |
2007年 | 766篇 |
2006年 | 728篇 |
2005年 | 573篇 |
2004年 | 526篇 |
2003年 | 472篇 |
2002年 | 408篇 |
2001年 | 372篇 |
2000年 | 341篇 |
1999年 | 315篇 |
1998年 | 204篇 |
1997年 | 188篇 |
1996年 | 175篇 |
1995年 | 153篇 |
1994年 | 115篇 |
1993年 | 105篇 |
1992年 | 132篇 |
1991年 | 110篇 |
1990年 | 96篇 |
1989年 | 58篇 |
1988年 | 46篇 |
1987年 | 50篇 |
1986年 | 25篇 |
1985年 | 26篇 |
1984年 | 16篇 |
1983年 | 20篇 |
1982年 | 4篇 |
1980年 | 4篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1974年 | 1篇 |
1972年 | 1篇 |
1967年 | 2篇 |
1966年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
61.
Burmite (Burmese amber) from the Hukawng Valley in northern Myanmar is a remarkable valuable and obviously the most important amber for studying terrestrial diversity in the mid-Cretaceous.The diversity of Burmite inclusions is very high and many new taxa were found,including new order,new family/subfamily,and new genus.Till the end of 2016,14 phyla,21 classes,65 orders,279 families,515 genera and 643 species of organisms are recorded,which are summized and complied in this catalogue.Among them,587 species are arthropods.In addtion,the specimens which can not be identified into species are also listed in the paper.The information on type specimens,other materials,host and deposition of types are provided. 相似文献
62.
Yongmei Guo Sumei Yan Jian Gong Lu Jin Binlin Shi 《Biological trace element research》2018,184(1):75-82
To elucidate the effect of selenium (Se) on antioxidant function of mammary glands in dairy cows and the underlying mechanism, an experiment was conducted using a single-factor completely randomized design study. Bovine mammary epithelial cells (BMECs) were randomly divided into four groups: control, Se treatment, 2,4-dinitrochlorobenzene (DNCB) inhibition, and Se prevention. Treatment of BMECs with Se was found to significantly reverse decreased cell proliferation and the expression of thioredoxin reductase (TrxR) after DNCB exposure. DNCB-induced activation of apoptosis signaling kinase-1 (ASK-1), which activates the mitogen-activated protein kinase (MAPK) pathway, was reduced in BMECs treated with Se. Additionally, our results indicated that Se treatment resulted in lower intracellular accumulation of arachidonic acid (ARA) and 15-hydroperoxyeicosatetraenoic acid (15-HPETE) due to suppressed expression of cytosolic phospholipase A2 (cPLA2) regulated by p38MAPK and c-Jun N-terminal kinase (JNK) in DNCB-stimulated BMECs. Taken together, these findings suggest that Se treatment improved the antioxidant function of dairy cow mammary glands and protected cells from oxidative damage primarily by increasing the activity of TrxR, inhibiting the activation of the MAPK signaling pathway, and thus decreasing the content of ARA and its related metabolites. 相似文献
63.
Tumor necrosis factor-alpha enhances inhibitory effects of interleukin-1 beta on Leydig cell steroidogenesis 总被引:1,自引:0,他引:1
J H Calkins H Guo M M Sigel T Lin 《Biochemical and biophysical research communications》1990,166(3):1313-1318
Human recombinant tumor necrosis factor-alpha (rTNF alpha) alone (up to 1000 units/ml) did not alter either basal or human chorionic gonadotropin (hCG)-induced testosterone formation in primary culture of rat Leydig cells. However, concomitant addition of rTNF alpha with human recombinant interleukin-1 beta (rIL-1 beta) enhanced the inhibitory effects of rIL-1 beta. The rIL-1 beta dose response curve was shifted to the left (IC50 changed from 1 ng/ml to 0.3 ng/ml). Even though rTNF alpha had no effect on testosterone formation, hCG-stimulated cyclic AMP formation was inhibited by rTNF alpha in a dose dependent manner. In the presence of both rTNF alpha and rIL-1 beta, hCG-induced cyclic AMP formation and binding of [125I]-hCG to Leydig cells were further inhibited. Testicular macrophages represent about 20% of the interstitial cells. TNF alpha and IL-1 may be produced locally by interstitial macrophages and have paracrine effects on Leydig cell function. 相似文献
64.
Tomohiro Teraminami Atsushi Nakashima Mao Ominami Masanori Yamamoto Zhang Guo Sheng Ken Yoshikawa 《Landscape and Ecological Engineering》2013,9(2):249-257
Salix cheilophila Schneid. is a naturally occurring Salix species in Mu Us Sandy Land, Inner Mongolia, China. We focused on the morphological adaptability of S. cheilophila to sand dune burial. For morphological measurements, 32 S. cheilophila seedlings were removed from a community which was in the process of being buried by a shifting sand dune. Each seedling collected included the entire root system. We measured the number, length, and biomass of the adventitious roots, primary lateral roots, and taproot, and compared the morphological characteristics of the root system, including adventitious roots, for seedlings buried to various levels in the sand. The growth range of adventitious roots increased as the length of the buried portion of the main shoot increased. In addition, the total dry weight of all current-year shoots tended to increase gradually with increasing total dry weight of the adventitious roots. These results suggest that S. cheilophila tends to make use of the sedimentary sand layer that accompanies shifting sand dunes. However, there was no correlation between biomass or number of adventitious roots and the length of the buried part of the main shoot. Thus, S. cheilophila does not grow adventitious roots proportional to the buried part. These morphological characteristics of the root system, including the adventitious roots, may indicate that S. cheilophila has poor morphological adaptability to sand dune burial. 相似文献
65.
Qiupeng Zheng Jing Du Zhaofeng Zhang Jianhua Xu Lingyuan Fu Yunlei Cao Xianliang Huang Lingli Guo 《Gene》2013
Vascular malformations (VMs) are common congenital and neonatal dysmorphogenesis. VMs mostly occur sporadically with a few exceptions of inheritability. Tie2/angiopoietins-2 (Ang-2) and VEGF/KDR pathways are known to be involved in normal and pathogenic angiogenesis. Our study was aimed to test the contribution of these pathway gene variants to VMs. A total of 8 variants were found among 103 VM patients and 142 healthy controls. These variants comprised rs638203, rs639225, rs80338908 and rs80338909 in Tie2 gene, rs1870377 and rs2305949 in KDR gene, rs79337921 and rs34590960 in ANTXR1 gene. Our results indicated that rs638203 (p = 0.029) and rs639225 (p = 0.018) in Tie2 gene were associated with VM. A further bioinformatics analysis suggested the rs638203-G and rs639225-G might cause an abnormal splicing of Tie2 gene into to a defective protein. Our results identified two novel Tie2 gene polymorphisms with genetic susceptibility to VMs, although future functional validation of the two polymorphisms is warranted in the future. 相似文献
66.
67.
The reliability and durability of lithium‐ion capacitors (LICs) are severely hindered by the kinetic imbalance between capacitive and Faradaic electrodes. Efficient charge storage in LICs is still a huge challenge, particularly for thick electrodes with high mass loading, fast charge delivery, and harsh working conditions. Here, a unique thermally durable, stable LIC with high energy density from all‐inorganic hydroxyapatite nanowire (HAP NW)‐enabled electrodes and separators is reported. Namely, the LIC device is designed and constructed with the electron/ion dual highly conductive and fire‐resistant composite Li4Ti5O12‐based anode and activated carbon‐based cathode, together with a thermal‐tolerant HAP NW separator. Despite the thick‐electrode configuration, the as‐fabricated all HAP NW‐enabled LIC exhibits much enhanced electrochemical kinetics and performance, especially at high current rates and temperatures. Long cycling lifetime and state‐of‐the‐art areal energy density (1.58 mWh cm?2) at a high mass loading of 30 mg cm?2 are achieved. Benefiting from the excellent fire resistance of HAP NWs, such an unusual LIC exhibits high thermal durability and can work over a wide range of temperatures from room temperature to 150 °C. Taking full advantage of synergistic configuration design, this work sets the stage for designing advanced LICs beyond the research of active materials. 相似文献
68.
69.
Pectinase was immobilized on a sodium alginate support using glutaraldehyde and retained 66% activity. The optimal pH for
activity shifted from 3.0 to 3.5 after immobilization; however, the optimum temperature remained unchanged at 40°C. The immobilized
enzyme also had a higher thermal stability and reusability than the free enzyme, and retained 80% of initial activity after
11 batch reactions. 相似文献
70.
An orthologue of the vacuolar Na+/H+ antiporter gene, AmNHX2, was isolated from a desert plant, Ammopiptanthus mongolicus, by RACE-PCR. It has a total length of 1,986 bp, with an open reading frame of 1,632 bp, encoding a predicted polypeptide
of 543 amino acids. Sequence similarity and exon constituent analysis clearly suggested that AmNHX2 encoded an AtNHX2 (an antiporter from Arabidopsis) like vacuolar Na+/H+ antiporter. AmNHX2 could be strongly induced by both drought and salt stress. Heterologous expression in the yeast mutant nhx1 indicated that AmNHX2 was the orthologue of ScNHX1, and the complementation effect was almost the same as AtNHX1. Over-expressing AmNHX2 resulted in enhanced tolerances to both drought and salt stresses in transgenic Arabidopsis plants. The transgenic plants
accumulated lower Na+ content in their leaves, showing healthier root system after salt stress, and retained more water during the drought stress.
Our work suggested that AmNHX2 was a salt tolerance determinant in A. mongolicus, but might not be a contributor to the difference in salt sensitivity between A. thaliana and A. mongolicus. 相似文献