全文获取类型
收费全文 | 2100篇 |
免费 | 221篇 |
国内免费 | 173篇 |
出版年
2024年 | 10篇 |
2023年 | 37篇 |
2022年 | 63篇 |
2021年 | 112篇 |
2020年 | 82篇 |
2019年 | 113篇 |
2018年 | 130篇 |
2017年 | 78篇 |
2016年 | 110篇 |
2015年 | 158篇 |
2014年 | 165篇 |
2013年 | 152篇 |
2012年 | 184篇 |
2011年 | 139篇 |
2010年 | 87篇 |
2009年 | 78篇 |
2008年 | 99篇 |
2007年 | 94篇 |
2006年 | 84篇 |
2005年 | 67篇 |
2004年 | 62篇 |
2003年 | 69篇 |
2002年 | 84篇 |
2001年 | 41篇 |
2000年 | 30篇 |
1999年 | 29篇 |
1998年 | 23篇 |
1997年 | 15篇 |
1996年 | 16篇 |
1995年 | 10篇 |
1994年 | 12篇 |
1993年 | 5篇 |
1992年 | 3篇 |
1991年 | 15篇 |
1990年 | 3篇 |
1989年 | 5篇 |
1988年 | 2篇 |
1987年 | 5篇 |
1985年 | 4篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有2494条查询结果,搜索用时 31 毫秒
981.
Hongxiang Zhang Stephen P. Bonser Si‐Chong Chen Timothy Hitchcock Angela T. Moles 《Austral ecology》2018,43(1):69-75
We provide a large‐scale quantification of the relationship between latitude and the proportion of species with clonal reproduction. Parasite pressure is thought to be higher at low latitudes, while abiotic stress is thought to be higher at high latitudes. We therefore predicted that there would be a higher proportion of clonal species at high latitudes than at low latitudes. We collected data of 4386 native seed plant species from 446 genera and 99 families present in ABRSFlora of Australia. Species' occurrence records were taken from the Atlas of Living Australia, including 817 450 species‐site combinations spanning 34.5° of latitude. Logistic regression showed that the proportion of clonal species significantly increased with latitude, rising from 3.3% clonal species at 9.25°S to 26.7% clonal species at 43.75°S. The overall average proportion of clonal species in Australian seed plants was 9.4%. This study adds to our growing understanding of dramatic latitudinal gradients in the way plants grow and reproduce. It also reveals that Australian vegetation contains a relatively low proportion of clonally reproducing species. 相似文献
982.
Several methods including microwave, Frenchpress, autoclave, bead-beating, ultrasonication, and osmotic shock were compared to identify the most effective microalgal cell disruption method. Botryococcus braunii LB572 was cultured in 5 L flasks containing JM medium mixed with oceanic sediment extract for 13 days. Among the methods tested, enhanced lipid extraction was achieved through microwave treatment (2450MHz, 1250W at 150°C for 20 min). Oleic (C18:1), linolenic (C18:3), and palmitic acids (C16:0) were found to be the major fatty acids among the C14-C24 acids from extracted lipid. In addition, the optimal conditions of transesterification were as follows: 70 mL of methanol, 6 mL of sulfuric acid, 8 mL of chloroform, and boiling at 100°C for 30 min; 85.4% of C14-C24 FAME and 78.5% of C16-C18 FAME were esterified from transesterifiable lipids. 相似文献
983.
D. H. Gong G. Z. Wang W. T. Si Y. Zhou Z. Liu J. Jia 《Russian Journal of Plant Physiology》2018,65(1):98-103
The effects of NaCl and Na2SO4 on photosynthetic pigments, malondialdehyde (MDA), Rubisco activity and superoxide dismutase (SOD) activity were investigated in Kalidium foliatum (Pall.) Moq., which is distributed in the saline soil of Hetao irrigation area in Inner Mongolia China. The K. foliatum plants were treated with NaCl (0, 100, 250, 400 and 500 mM), Na2SO4 (0, 100, 250, 400 and 500 mM) and NaCl + Na2SO4 (1: 1, v/v) (0, 100, 250, 400 and 500 mM of Na+ concentration, 0, 50, 125, 200 and 250 mM of Cl– and SO 4 2– concentration) for 10 days. Content of chlorophylls and carotenoids were significantly higher than control at increasing NaCl and Na2SO4 concentration, in contrast, were significantly reduced by higher concentration of NaCl + Na2SO4. Rubisco activity reduced steadily at 100 and 250 mM NaCl, while increased at 400 and 500 mM NaCl. Rubisco activity was significantly higher than control at 100 mM Na2SO4, and was no more change under NaCl + Na2SO4 treatment. The SOD activity increased with increasing NaCl and Na2SO4, and increased at moderate NaCl + Na2SO4 treatment. MDA content was lower than control at 250 mM salt concentration. On the basis of the data obtained, K. foliatum showed resistance to salt such as Na+, Cl–and SO 4 2– , Rubisco activity in K. foliatum might be more sensitive to salt. 相似文献
984.
Engineering Temperature‐Dependent Carrier Concentration in Bulk Composite Materials via Temperature‐Dependent Fermi Level Offset 下载免费PDF全文
Si Hui Wenpei Gao Xu Lu Anurag Panda Trevor P. Bailey Alexander A. Page Stephen R. Forrest Donald T. Morelli Xiaoqing Pan Kevin P. Pipe Ctirad Uher 《Liver Transplantation》2018,8(3)
Precise control of carrier concentration in both bulk and thin‐film materials is crucial for many solid‐state devices, including photovoltaic cells, superconductors, and high mobility transistors. For applications that span a wide temperature range (thermoelectric power generation being a prime example) the optimal carrier concentration varies as a function of temperature. This work presents a modified modulation doping method to engineer the temperature dependence of the carrier concentration by incorporating a nanosize secondary phase that controls the temperature‐dependent doping in the bulk matrix. This study demonstrates this technique by de‐doping the heavily defect‐doped degenerate semiconductor GeTe, thereby enhancing its average power factor by 100% at low temperatures, with no deterioration at high temperatures. This can be a general method to improve the average thermoelectric performance of many other materials. 相似文献
985.
正The Society for Invertebrate Pathology (SIP) is foremost in the world covering all aspects of related research in insect virology, bacteriology, mycology, parasitology and microbial control. The SIP has a wide scientific appeal with members from many countries spanning every continent in the globe. Election of members to the Society’s Governing 相似文献
986.
ChuanLiang Cui Li Zhou Bin Lian Lu Si XiNan Sheng ZhiHong Chi Yan Kong Xuan Wang BiXia Tang LiLi Mao SiMing Li Jie Dai XieQiao Yan Xue Bai Jun Guo 《Translational oncology》2018,11(5):1155-1159
OBJECTIVE: Asian melanoma patients, predominantly comprised of acral and mucosal subtypes, might not benefit from immunotherapy and targeted therapy as much as Caucasian patients. Novel treatment strategies are demanded after conventional treatment failure. This was a prospective, single-arm, and single-center dose escalation study to investigate the safety and preliminary efficacy of apatinib combined with temozolomide in heavily treated advanced melanoma patients. METHODS: Patients were sequentially admitted to four dose-escalating groups of apatinib and temozolomide (three cases in each group) using a traditional 3?+?3 dose escalation design method. RESULTS: Twelve patients were enrolled between December 2016 and August 2017. Most patients with an acral or mucosal primary origin progressed after immunotherapy or targeted therapy. Dose escalation had been completed without dose-limiting toxicity. Common adverse events included hypertension, hand-foot syndrome, proteinuria, neutropenia, nausea, and fatigue. All adverse events were grade 1 or 2, while the maximum tolerated dose was not reached. Up to January 2018, 1 patient achieved partial response, 9 experienced stable disease, and 2 exhibited progressive disease. The objective response rate and disease control rate were 8.3% and 83%, respectively. CONCLUSIONS: In conclusion, apatinib combined with temozolomide was well tolerated and has demonstrated efficacy in advanced melanoma patients. 相似文献
987.
Siân Waters Tamlin Watson Sandra Bell Joanna M. Setchell 《European Journal of Wildlife Research》2018,64(6):69
Conservationists consider open and direct communication as best practice even when their data conflict with local beliefs. However, ensuring the effective delivery of a controversial message without overtly challenging community identity is difficult. Such a scenario needs high levels of meaningful contact and trust-building dialogue between conservationists and communities as well as innovative means of communicating controversial information. Indirect communication is one such strategy, allowing people to draw their own conclusions about controversial information. We present an example of successful indirect communication of such information in the context of a long-term Barbary macaque community conservation project in Morocco. Dogs in the area kill macaques and domestic livestock in the forest, and local shepherds believed these dogs to be feral. However, our observations identified these dogs as being owned, free-roaming village dogs rather than feral dogs. To impart this controversial information, we developed a dog health programme to communicate our findings and improve the health of domestic dogs to safeguard human and animal health. We administered rabies vaccinations to dogs in three villages and provided their owners with brightly coloured dog collars. After observing collared dogs hunting in the forest, the shepherds realised the dogs had owners. Community participation was high and we vaccinated 242 dogs achieving 60–81% vaccination coverage. An additional benefit of the activity was to successfully convey the message that the conservation team is committed to local people’s welfare as well as to Barbary macaque conservation. 相似文献
988.
Three new iridoids named as pediverticilatasin A – C ( 1 – 3 , resp.), together with five known iridoids ( 4 – 8 , resp.) were isolated from the whole plants of Pedicularis verticillata. The structures of three new compounds were identified as (1S,7R)‐1‐ethoxy‐1,5,6,7‐tetrahydro‐7‐hydroxy‐7‐methylcyclopenta[c]pyran‐4(3H)‐one ( 1 ), (1S,4aS,7R,7aS)‐1‐ethoxy‐1,4a,5,6,7,7a‐hexahydro‐7‐hydroxy‐7‐methylcyclopenta[c]pyran‐4‐carboxylic acid ( 2 ), (1S,4aS,7R,7aS)‐1‐ethoxy‐1,4a,5,6,7,7a‐hexahydro‐7‐hydroxy‐7‐methylcyclopenta[c]pyran‐4‐carbaldehyde ( 3 ). Their structures were elucidated on the basis of spectroscopic methods and compared with the NMR spectra data in the literature. All compounds were evaluated for their anti‐complementary activity on the classical pathway of the complement system in vitro. Among which, compounds 1 , 3 , and 6 exhibited anti‐complementary effects with CH50 values ranging from 0.43 to 1.72 mm , which are plausible candidates for developing potent anti‐complementary agents. 相似文献
989.
Bo Si Oh Paul G. Twigg Jeong Soo Hong Beth C. Mullin Chung Sun An 《Physiologia plantarum》1997,99(4):707-713
The organization of genes with the capacity to code for four proteins involved in nitrogen fixation in Frankia strain FaC1 was determined by restriction fragment mapping and nucleotide sequence analysis. Analysis of the 44-kb genomic cosmid clone pFAH 1. isolated from a cosmid library made from Frankia strain FaCl, resulted in the identification of a 7.2-kb Pst I fragment to which Klebsiella nif H, nif D and nif K probes hybridized. This nif -hybridizing fragment was subcloned and analyzed by restriction fragment mapping. Further subcloning of the 7.2-kb fragment and subsequent sequence analysis of approximately 6.8 kb revealed the presence of six open reading frames (ORFs). Four of these ORFs have the potential to code for nif V-, nif H-, nif D- and nif K-like gene products and the two others are unidentified ORFs. The organization of the structural genes for nitrogenase is the same in this Frankia strain as it is in most other nitrogen-fixing prokaryotes, but the positioning of the nif V-like gene relative to the nif HDK cluster differs, A consensus nif -promoter-like sequence, found 5'to nif H. was not detected upstream of the nif V-like gene. Nine copies of a 7-bp direct repeat were found 5'to ORFA. 相似文献
990.
柱前衍生氨基酸的高效液相色谱分析 总被引:4,自引:1,他引:3
综述了目前柱前衍生氨基酸高效液相色谱分析技术的最新进展和现状,分别详细介绍了应用最广、技术最先进的几种柱前衍生氨基酸分析技术和方法。 相似文献