全文获取类型
收费全文 | 12870篇 |
免费 | 493篇 |
国内免费 | 738篇 |
专业分类
系统科学 | 637篇 |
丛书文集 | 293篇 |
教育与普及 | 126篇 |
理论与方法论 | 61篇 |
现状及发展 | 1039篇 |
研究方法 | 43篇 |
综合类 | 11891篇 |
自然研究 | 11篇 |
出版年
2024年 | 64篇 |
2023年 | 140篇 |
2022年 | 193篇 |
2021年 | 165篇 |
2020年 | 155篇 |
2019年 | 93篇 |
2018年 | 115篇 |
2017年 | 139篇 |
2016年 | 204篇 |
2015年 | 367篇 |
2014年 | 425篇 |
2013年 | 370篇 |
2012年 | 534篇 |
2011年 | 606篇 |
2010年 | 443篇 |
2009年 | 427篇 |
2008年 | 393篇 |
2007年 | 395篇 |
2006年 | 353篇 |
2005年 | 529篇 |
2004年 | 868篇 |
2003年 | 1115篇 |
2002年 | 1185篇 |
2001年 | 1000篇 |
2000年 | 636篇 |
1999年 | 518篇 |
1998年 | 203篇 |
1997年 | 235篇 |
1996年 | 174篇 |
1995年 | 155篇 |
1994年 | 155篇 |
1993年 | 150篇 |
1992年 | 152篇 |
1991年 | 117篇 |
1990年 | 109篇 |
1989年 | 125篇 |
1988年 | 93篇 |
1987年 | 60篇 |
1986年 | 48篇 |
1985年 | 50篇 |
1979年 | 61篇 |
1974年 | 56篇 |
1973年 | 49篇 |
1972年 | 50篇 |
1971年 | 66篇 |
1970年 | 54篇 |
1969年 | 68篇 |
1968年 | 59篇 |
1966年 | 55篇 |
1965年 | 41篇 |
排序方式: 共有10000条查询结果,搜索用时 656 毫秒
991.
CHEN Yaning CHEN Yapeng LI Weihong & ZHANG Hongfeng Xinjiang Institute of Ecology Geography Chinese Academy of Sciences Urumqi China Correspondence should be addressed to Chen Yaming 《科学通报(英文版)》2003,48(18):1995-1999
The content of proline in the plant bodies is closely related to the converse-succession-resistant capability of plants. Under the drought stress, the proline accumulates rapidly in the plant bodies for maintaining a certain mois-ture content and an expanding-pressure momentum in cells through the osmoregulation, thus the drought-resis- tant capability and the converse-succession-resistant ca-pability of plants are increased[1,2]. Many researches on the relationship between the proline and the… 相似文献
992.
WANGTiejun QIYingqun XUJingkun HUXiujie CHENPing 《科学通报(英文版)》2003,48(22):2444-2445
By mixing various concentrations of poly (ethylene glycol), a series of poly(3,4-ethylenedioxythiophene)-poly(styeenesuffonate) composite thin films were prepared.The electrical conductivity of the PEDOT-PSS/PEG thin films was measured by the four-pcobe method. Experimental results showed that the inclusion of poly(ethylene glycol) influenced the electrical conductivity of PEDOT-PSS film significantly. With the increase of PEG concentrations, the electrical conductivity sharply increased to reach a maximum and then slowly decreased down. Furthermore, the PEG molecular weight and environment temperature also played important roles on the electrical conductivity of PEDOT-PSS/PEG thin films. A good linear relationship was found between in σDC and T^-1/2 within the entire temperature range detected. 相似文献
993.
DING Bin WANG Hongmei YI Long CHENG Peng LI Licun ZHAI Yuping LIAO Daizheng YAN Shiping & JIANG Zonghui Department of Chemistry Nankai University Tianjin China Correspondence should be addressed to Cheng Peng or Liao Daizheng 《科学通报(英文版)》2003,48(22):2446-2449
Spin-crossover complexes are of great interest to the scientists because of their potential application in molecular-based electronic devices. Some octahedral metal compounds with 3dn (4 ≤ n ≤ 7) configuration can induce a spin state conversion through a fine tuning condition (temperature, pressure, light irradiation, etc.). If the conversion occurs reversibly with a hystersis loop and color change, it will make the system possessing memory effect. The memory effect can be magnified and the … 相似文献
994.
DINGJie ZHUTong 《科学通报(英文版)》2003,48(21):2267-2276
Fine particles play an important role in the atmosphere. Research on heterogeneous reactions on the surface of fine particles is one of the frontier areas of atmospheric science. In this paper, physical and chemical characteristics of fine particles in the atmosphere and the interactions between trace gases and fine particles are described, methods used in heterogeneous reactions research are discussed in detail, progress in the study of heterogeneous reactions on the surface of fine particles in the atmosphere is summarized, existing important questions are pointed out and future research directions are suggested. 相似文献
995.
WURongcheng QUJiuhu HEHong YUYunbo 《科学通报(英文版)》2003,48(21):2311-2316
CuO-Fe2O3 composite material with strong magnetism and a large surface area is prepared by the co-precipitate method. Its adsorption properties towards Acid Red B (ARB) and the regeneration by catalytic combastion of organic compounds have been studied. The results show that the prepared CuO-Fe2O3 composite is an excellent adsorbent for ARB adsorption at acid condition. The presence of Cl^- has no effect on ARB adsorption. But the SO4^2- can inhibit ARB adsorption. After being recovered by the magnetic separation method, the adsorbent can be regenerated by catalytic oxidation of absorbate at 300℃ in air atmosphere. The combustion reactions of ARB in the presence or absence of CuO-Fe2O3 are studied by in situ diffuse refieclion FTIR. The results indicate that, in the presence of CuO-Fe2O3, the degradation temperature is significantly lowered by the catalysis of CuO-Fe2O3, and ARB can be oxidized completely without volatile organic compound by-product; in comparison, in the absence of CuO-Fe2O3, the temperature needed for oxidation of ARB is higher and the reaction is incomplete with some N-containing harmful compounds produced. The reusability of CuO-Fe2O3 is also studied in successive seven adsorption-regeneration cycles. 相似文献
996.
WANGWei NINGXinbao WANGJun ZHANGSheng CHENJie LILejia 《科学通报(英文版)》2003,48(16):1700-1703
Muitifractai characteristics of 16-channel human electroencephalogram (EEG) signals under eye-closed rest are analyzed for the first time. The result shows that the EEGs from the different sites on the scalp have different muitifractai characteristics and the muitifractai strength value △α exhibits a kind of interleaving and left-right opposite distribution on scalp. This distribution rule is consistent with the localization of function and the iateralization theory in physiology. So △α can become an effective parameter to describe the brain potential character. And such a △α stable distribution rule on sites of the scalp means a classic cerebral cortex active state. 相似文献
997.
曹禺的《雷雨》从问世以来,就一直处在不断的争论之中,但它仍然获得了“精品”、“经典”的美誉。然而,《雷雨》表现的主题,描写的主要人物以及运用的艺术技巧表明:《雷雨》是一部思想上极其幼稚、单纯,艺术上极其笨拙、不成熟的作品。有必要将其还原到曹禺当时的思想实际和创作实际中。 相似文献
998.
QTL mapping of the root traits and their correlation analysis with drought resistance using DH lines from paddy and upland rice cross 总被引:8,自引:0,他引:8
MUPing LIZichao LIChunping ZHANGHongliang WUChangming LIChen WANGXiangkun 《科学通报(英文版)》2003,48(24):2718-2724
A Double Haploid (DH) population, 116 plants, derived from the cross between Japonica upland rice IRAT109 and paddy rice Yuefu, planted in PVC pipe under upland ecosystem in 2001 and 2002, was used in this study. Seven root traits, including basal root thickness (BRT), total root number (RN), maximum root length (MRL), root fresh weight (RFW), root dry weight (RDW), ratio of root fresh weight to shoot fresh weight (RFW/SFW) and ratio of root dry weight to shoot dry weight (RDW/SDW), were studied. Using index of drought resistance (IDR), the ratio of yield under upland ecosystem to yield under lowland ecosystem of DH lines, as the criteria of drought resistance, and correla-tion analysis between root traits and IDR, showed that BRT, MRL and RN were significantly correlated with IDR. High IDR lines had thicker BRT, longer MRL and less RN than low IDR lines. A molecular linkage map with 94 RFLP markers and 71 SSR markers covering 1535.1 cM was pro-duced. QTLs and G譋 interactions for BRT, RN, MRL, RFW, RDW, RFW/SFW and RDW/SDW were obtained based on the constructed molecular linkage map and soft-ware QTLmapper version 1.0. A total of 18 additive QTLs and 18 pairs of epistatic QTLs associated with root traits were detected. There were nine additive QTLs and two pairs of epistatic QTLs performed significant interactions with environment. Some QTLs with high general contribution and no G譋 interaction were obtained. Two pairs of epistatic QTLs mrl3 and mrl8, brt3 and brt11a controlling MRL and BRT had high general contributions of 21.51% and 13.03% respectively. An additive QTL and a pair of epistatic QTLs controlling RFW and RDW had high general contributions of 13.50% and 25.64% respectively. Marker assisted selec-tion (MAS) for rice drought resistance based on QTL with high general contribution, low G譋 interaction and tightly linkage with IDR were also discussed. 相似文献
999.
The effect of sodium nitroprusside (SNP), a donor of nitric oxide, on meiotic maturation of mouse oocytes was studied by injecting Nw-nitro-L-arginine methyl ester (L-NAME) intra-peritoneal (ip), a nitric oxide synthase inhibitor, or culturing oocytes in the medium supplemented with L-NAME or hypoxanthine (HX) to arrest the spontaneous oocyte maturation in vitro. The results showed that the inhibitory effect of L-NAME by injecting 10 mg/kg ip on extrusion of the first polar body only could be reversed by injecting 2.5 mg/kg SNP with L-NAME simultaneously (P < 0.05). Half an hour later ten mice died when given 10 mg/kg SNP ip. The treatment of some concentrations of SNP (10–7, 10–6, 10–5mol/L) significantly stimulated meiotic maturation to metaphase Ⅱ stages in cumulus enclosed oocytes in the presence of HX. However, other concentrations of SNP (10–8, 10–4, 10–3 mol/L) had no effect on HX-arrested oocyte meiotic maturation. The optimal concentration of SNP on CEOs had no effect on DOs. The dose of 10–3 mol/LL-NAME demonstrated a significant suppression in formation of PB1, but not in GVBD. This inhibition was reversed by the addition of SNP. These results indicated that the physiological levels of NO produced by cumulus cells could stimulate meiotic maturation of mouse oocytes both in vivo and in vitro. 相似文献
1000.
XIEWenwei GUOYanchuan GANChangsheng YANTiantang PANZhongxiao PENGBixian 《科学通报(英文版)》2003,48(5):424-429
A series of 1,8,15,22-tetra(2,4-ditertbutylphen-oxy) phthalocyanines [α-(oAr)4PcM,M1=(H)2,M2=Pd,M3=Cu,M4=Zn,M5=Pb] were synthesized in this study.Each compound was bromized in two kinds of solvent.One is the solvent mixture of 1,1,2-trichloroethane and water,the other is 1,1,2-trichloroethane alone.The effects of solvent,bromine excess added and reaction duration on the bromization reaction were studied.The shift of maximum absorbance wave-length both is solution and in solid thin film was investigated comparatively,discovering that both were bathochromism but the former was more.TG data showed that the temperature of thermal decomposition decreased continuously with the increase of numbers of bromine.Finally,the fragments produced during the bromization of (OAr)4PcPb in 1,1,2-trichloroethane were characterized by GC/MS.Based on the electronic structure,the possible mechanism of decomposition of these compounds was presented and discussed. 相似文献