全文获取类型
收费全文 | 8231篇 |
免费 | 400篇 |
国内免费 | 39篇 |
出版年
2024年 | 15篇 |
2023年 | 117篇 |
2022年 | 201篇 |
2021年 | 571篇 |
2020年 | 263篇 |
2019年 | 323篇 |
2018年 | 408篇 |
2017年 | 288篇 |
2016年 | 408篇 |
2015年 | 491篇 |
2014年 | 552篇 |
2013年 | 675篇 |
2012年 | 633篇 |
2011年 | 577篇 |
2010年 | 345篇 |
2009年 | 302篇 |
2008年 | 317篇 |
2007年 | 300篇 |
2006年 | 254篇 |
2005年 | 221篇 |
2004年 | 160篇 |
2003年 | 125篇 |
2002年 | 120篇 |
2001年 | 62篇 |
2000年 | 69篇 |
1999年 | 54篇 |
1998年 | 41篇 |
1997年 | 21篇 |
1996年 | 30篇 |
1995年 | 30篇 |
1994年 | 18篇 |
1993年 | 23篇 |
1992年 | 43篇 |
1991年 | 55篇 |
1990年 | 44篇 |
1989年 | 41篇 |
1988年 | 34篇 |
1987年 | 47篇 |
1986年 | 34篇 |
1985年 | 40篇 |
1984年 | 31篇 |
1983年 | 23篇 |
1982年 | 22篇 |
1981年 | 16篇 |
1980年 | 15篇 |
1979年 | 24篇 |
1978年 | 26篇 |
1975年 | 14篇 |
1974年 | 16篇 |
1973年 | 20篇 |
排序方式: 共有8670条查询结果,搜索用时 390 毫秒
991.
Khalid Mahmood Zia Mohammad ZuberAli Rizwan Tahir JamilShazia Tabasum Muhammad Shahid 《Carbohydrate polymers》2012,87(3):2063-2067
A series of poly(vinyl alcohol) of different commercial grades were prepared and applied onto the surfaces of cotton and blends of cotton/polyester fibers. The molecular structure was confirmed using Fourier Transform Infrared spectroscopy. Physicochemical properties such as viscosity and solid contents (%) were determined and discussed. Factors affecting the performance properties of the finished substrate such as post-treatment with poly(vinyl alcohol) of different grades, concentration and dilutions were studied. Fixation of the poly(vinyl alcohol) onto/or within the cellulose structure is accompanied by the formation of semi-inter-penetrated network structure thereby enhancing the association as well as providing very high stiffness. The results revealed that applications of poly(vinyl alcohol) on the textile fabrics in the finishing processes enables to enhance the stiffness as well as helps to improve its pilling resistance. 相似文献
992.
Mohammad ZuberKhalid Mahmood Zia Ijaz Ahmad BhattiTahir Jamil Fazal-ur-RehmanAli Rizwan 《Carbohydrate polymers》2012,87(4):2439-2446
A series of aqueous solutions of poly(vinyl alcohol) of various commercial products were prepared and applied onto the surfaces of cotton and blends of cotton/polyester fabrics. Fourier transform infrared spectrophotometer was used to confirm the molecular structure of the polyvinyl alcohol used. Performance tests such as colorfastness to rubbing (dry and wet) and colorfastness to washing were determined. The controlling variables affecting the performance properties of the finished substrate such as post-treatment with poly(vinyl alcohol) of various commercial trades, concentration and dilutions were studied. Crocking, washing and hue change of the treated dyed and printed fabrics is accompanied by the formation of semi-inter-penetrated network structure due to the presence of the hydroxyl (-OH) groups which make feasible to a number of grafting and physical cross linking reactions of polymer backbone. 相似文献
993.
Khadem AF Wieczorek AS Pol A Vuilleumier S Harhangi HR Dunfield PF Kalyuzhnaya MG Murrell JC Francoijs KJ Stunnenberg HG Stein LY DiSpirito AA Semrau JD Lajus A Médigue C Klotz MG Jetten MS Op den Camp HJ 《Journal of bacteriology》2012,194(14):3729-3730
The draft genome of Methylacidiphilum fumariolicum SolV, a thermoacidophilic methanotroph of the phylum Verrucomicrobia, is presented. Annotation revealed pathways for one-carbon, nitrogen, and hydrogen catabolism and respiration together with central metabolic pathways. The genome encodes three orthologues of particulate methane monooxygenases. Sequencing of this genome will help in the understanding of methane cycling in volcanic environments. 相似文献
994.
Geobacillus thermoleovorans CCB_US3_UF5 is a thermophilic bacterium isolated from a hot spring in Malaysia. Here, we report the complete genome of G. thermoleovorans CCB_US3_UF5, which shows high similarity to the genome of Geobacillus kaustophilus HTA 426 in terms of synteny and orthologous genes. 相似文献
995.
Rinaldo-Matthis A Ahmad S Wetterholm A Lachmann P Morgenstern R Haeggström JZ 《Biochemistry》2012,51(4):848-856
Human leukotriene C? synthase (hLTC4S) is an integral membrane protein that catalyzes the committed step in the biosynthesis of cysteinyl-leukotrienes, i.e., formation of leukotriene C? (LTC?). This molecule, together with its metabolites LTD? and LTE?, induces inflammatory responses, particularly in asthma, and thus, the enzyme is an attractive drug target. During the catalytic cycle, glutathione (GSH) is activated by hLTC4S that forms a nucleophilic thiolate anion that will attack LTA?, presumably according to an S(N)2 reaction to form LTC?. We observed that GSH thiolate anion formation is rapid and occurs at all three monomers of the homotrimer and is concomitant with stoichiometric release of protons to the medium. The pK(a) (5.9) for enzyme-bound GSH thiol and the rate of thiolate formation were determined (k(obs) = 200 s?1). Taking advantage of a strong competitive inhibitor, glutathionesulfonic acid, shown here by crystallography to bind in the same location as GSH, we determined the overall dissociation constant (K(d((GS) = 14.3 μM). The release of the thiolate was assessed using a GSH release experiment (1.3 s?1). Taken together, these data establish that thiolate anion formation in hLTC4S is not the rate-limiting step for the overall reaction of LTC? production (k(cat) = 26 s?1), and compared to the related microsomal glutathione transferase 1, which displays very slow GSH thiolate anion formation and one-third of the sites reactivity, hLTC4S has evolved a different catalytic mechanism. 相似文献
996.
Kurek KC Luks VL Ayturk UM Alomari AI Fishman SJ Spencer SA Mulliken JB Bowen ME Yamamoto GL Kozakewich HP Warman ML 《American journal of human genetics》2012,90(6):1108-1115
Congenital lipomatous overgrowth with vascular, epidermal, and skeletal anomalies (CLOVES) is a sporadically occurring, nonhereditary disorder characterized by asymmetric somatic hypertrophy and anomalies in multiple organs. We hypothesized that CLOVES syndrome would be caused by a somatic mutation arising during early embryonic development. Therefore, we employed massively parallel sequencing to search for somatic mosaic mutations in fresh, frozen, or fixed archival tissue from six affected individuals. We identified mutations in PIK3CA in all six individuals, and mutant allele frequencies ranged from 3% to 30% in affected tissue from multiple embryonic lineages. Interestingly, these same mutations have been identified in cancer cells, in which they increase phosphoinositide-3-kinase activity. We conclude that CLOVES is caused by postzygotic activating mutations in PIK3CA. The application of similar sequencing strategies will probably identify additional genetic causes for sporadically occurring, nonheritable malformations. 相似文献
997.
Spiegel R Pines O Ta-Shma A Burak E Shaag A Halvardson J Edvardson S Mahajna M Zenvirt S Saada A Shalev S Feuk L Elpeleg O 《American journal of human genetics》2012,90(3):518-523
Degeneration of the cerebrum, cerebellum, and retina in infancy is part of the clinical spectrum of lysosomal storage disorders, mitochondrial respiratory chain defects, carbohydrate glycosylation defects, and infantile neuroaxonal dystrophy. We studied eight individuals from two unrelated families who presented at 2-6 months of age with truncal hypotonia and athetosis, seizure disorder, and ophthalmologic abnormalities. Their course was characterized by failure to acquire developmental milestones and culminated in profound psychomotor retardation and progressive visual loss, including optic nerve and retinal atrophy. Despite their debilitating state, the disease was compatible with survival of up to 18 years. Laboratory investigations were normal, but the oxidation of glutamate by muscle mitochondria was slightly reduced. Serial brain MRI displayed progressive, prominent cerebellar atrophy accompanied by thinning of the corpus callosum, dysmyelination, and frontal and temporal cortical atrophy. Homozygosity mapping followed by whole-exome sequencing disclosed a Ser112Arg mutation in ACO2, encoding mitochondrial aconitase, a component of the Krebs cycle. Specific aconitase activity in the individuals' lymphoblasts was severely reduced. Under restrictive conditions, the mutant human ACO2 failed to complement a yeast ACO1 deletion strain, whereas the wild-type human ACO2 succeeded, indicating that this mutation is pathogenic. Thus, a defect in mitochondrial aconitase is associated with an infantile neurodegenerative disorder affecting mainly the cerebellum and retina. In the absence of noninvasive biomarkers, determination of the ACO2 sequence or of aconitase activity in lymphoblasts are warranted in similarly affected individuals, based on clinical and neuroradiologic grounds. 相似文献
998.
MA Sobahan N Akter M Ohno E Okuma Y Hirai IC Mori Y Nakamura Y Murata 《Bioscience, biotechnology, and biochemistry》2012,76(8):1568-1570
Salinity significantly increased trisodium-8-hydroxy-1,3,6-pyrenetrisulphonic acid (PTS) uptake and decreased the K(+)/Na(+) ratio in salt-sensitive rice (Nipponbare) but did not markedly in salt-tolerant rice (Pokkali). Proline and glycinebetaine (betaine) suppressed the increase in PTS uptake and the decrease in the K(+)/Na(+) ratio in Nipponbare, but did not affect PTS uptake or the K(+)/Na(+) ratio in Pokkali. 相似文献
999.
Roel Bosma Ahmad Syafei Sidik Paul van Zwieten Anugrah Aditya Leontine Visser 《Wetlands Ecology and Management》2012,20(2):89-99
Around 1990, when in other countries mangrove protection took off, massive conversion of mangrove forest into shrimp ponds
started in the Mahakam delta. To identify constraints to and options for sustainable management we analysed institutions and
constraints with stakeholders. In 3 sites we used participatory tools and a complementary survey to assess the livelihood
framework. Since 1970, ponds for shrimp farming gradually replaced 75% of mangrove forested area. After 2004, recovery of
mangrove took off, as, mainly due to low shrimp yields, ponds were abandoned. In 2008, 54% of the delta was dedicated to ponds
for shrimp production. Around 80% of livelihood activities of pond-farmers, pond caretakers, and fishermen was related to
mangroves. The involvement of men and women in these activities varied between sites and types. Poor households depended more
on mangroves. Most activities resulted in seasonal income peaks; only a few activities resulted in a full daily livelihood.
Ponds, on the other hand, provide 50% of households’ livelihood, but this remains vulnerable in the context of the risky shrimp
production. Skewed land holding, unequal sharing of benefits, competing claims and vested interests of stakeholders pose a
great challenge to a transition to a more sustainable use of the mangrove area. In particular, ponds located on peat soils
are non-sustainable and would require full restoration into mangrove; ponds on other soils could best be transformed into
a mixed mangrove-pond system using a ‘green-water’ technology. 相似文献
1000.
G protein-coupled receptors (GPCRs) are transmembrane proteins, which transduce signals from extracellular ligands to intracellular
G protein. Automatic classification of GPCRs can provide important information for the development of novel drugs in pharmaceutical
industry. In this paper, we propose an evolutionary approach, GPCR-MPredictor, which combines individual classifiers for predicting
GPCRs. GPCR-MPredictor is a web predictor that can efficiently predict GPCRs at five levels. The first level determines whether
a protein sequence is a GPCR or a non-GPCR. If the predicted sequence is a GPCR, then it is further classified into family,
subfamily, sub-subfamily, and subtype levels. In this work, our aim is to analyze the discriminative power of different feature
extraction and classification strategies in case of GPCRs prediction and then to use an evolutionary ensemble approach for
enhanced prediction performance. Features are extracted using amino acid composition, pseudo amino acid composition, and dipeptide
composition of protein sequences. Different classification approaches, such as k-nearest neighbor (KNN), support vector machine (SVM), probabilistic neural networks (PNN), J48, Adaboost, and Naives Bayes, have been used to classify GPCRs. The proposed hierarchical GA-based ensemble classifier exploits
the prediction results of SVM, KNN, PNN, and J48 at each level. The GA-based ensemble yields an accuracy of 99.75, 92.45, 87.80, 83.57, and 96.17% at the five levels, on
the first dataset. We further perform predictions on a dataset consisting of 8,000 GPCRs at the family, subfamily, and sub-subfamily
level, and on two other datasets of 365 and 167 GPCRs at the second and fourth levels, respectively. In comparison with the
existing methods, the results demonstrate the effectiveness of our proposed GPCR-MPredictor in classifying GPCRs families.
It is accessible at . 相似文献