全文获取类型
收费全文 | 16573篇 |
免费 | 1104篇 |
国内免费 | 6篇 |
专业分类
17683篇 |
出版年
2023年 | 152篇 |
2022年 | 299篇 |
2021年 | 560篇 |
2020年 | 401篇 |
2019年 | 509篇 |
2018年 | 640篇 |
2017年 | 548篇 |
2016年 | 758篇 |
2015年 | 949篇 |
2014年 | 1045篇 |
2013年 | 1203篇 |
2012年 | 1294篇 |
2011年 | 1199篇 |
2010年 | 740篇 |
2009年 | 659篇 |
2008年 | 789篇 |
2007年 | 770篇 |
2006年 | 693篇 |
2005年 | 602篇 |
2004年 | 562篇 |
2003年 | 481篇 |
2002年 | 408篇 |
2001年 | 276篇 |
2000年 | 245篇 |
1999年 | 210篇 |
1998年 | 86篇 |
1997年 | 87篇 |
1996年 | 66篇 |
1995年 | 65篇 |
1994年 | 62篇 |
1993年 | 61篇 |
1992年 | 111篇 |
1991年 | 92篇 |
1990年 | 69篇 |
1989年 | 80篇 |
1988年 | 73篇 |
1987年 | 86篇 |
1986年 | 72篇 |
1985年 | 60篇 |
1984年 | 62篇 |
1983年 | 42篇 |
1982年 | 33篇 |
1981年 | 32篇 |
1980年 | 26篇 |
1979年 | 52篇 |
1978年 | 29篇 |
1976年 | 30篇 |
1975年 | 35篇 |
1974年 | 25篇 |
1973年 | 46篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
102.
The olive fly (Bactrocera oleae) is the most important olive tree (Olea europaea) pest. In the Mediterranean basin, where 98?% of its main hosts are concentrated, it causes major agricultural losses, due to its negative effect on production and quality of both olive and olive oil. Previous phylogeographic analyses have established that Mediterranean olive fly populations are distinct from other Old World populations, but did not agree on the specific population substructure within this region. In order to achieve a higher resolution of the diversity of olive fly populations, particularly in Central and Western Mediterranean (home to 70?% of the world production), we comparatively analyzed a set of samples from Portugal in the context of published mitochondrial sequences across the species' worldwide range. Strong evidence of population substructure was found in the Central and Western Mediterranean area, with two clearly separate phylogenetic branches. Together with previously published data, our results strongly support the existence of at least three distinct Mediterranean populations of the olive fly, raise the possibility of additional regional substructure and suggest specific avenues for future research. This knowledge can be instrumental in the development of better management and control strategies for a major pest of Mediterranean agriculture. 相似文献
103.
Acharya U Edwards MB Jorquera RA Silva H Nagashima K Labarca P Acharya JK 《The Journal of cell biology》2006,173(1):69-82
Scramblases are a family of single-pass plasma membrane proteins, identified by their purported ability to scramble phospholipids across the two layers of plasma membrane isolated from platelets and red blood cells. However, their true in vivo role has yet to be elucidated. We report the generation and isolation of null mutants of two Scramblases identified in Drosophila melanogaster. We demonstrate that flies lacking either or both of these Scramblases are not compromised in vivo in processes requiring scrambling of phospholipids. Instead, we show that D. melanogaster lacking both Scramblases have more vesicles and display enhanced recruitment from a reserve pool of vesicles and increased neurotransmitter secretion at the larval neuromuscular synapses. These defects are corrected by the introduction of a genomic copy of the Scramb 1 gene. The lack of phenotypes related to failure of scrambling and the neurophysiological analysis lead us to propose that Scramblases play a modulatory role in the process of neurotransmission. 相似文献
104.
Marcelo Rodrigues Thales H. F. Costa Reginaldo Alves Festucci-Buselli Luzimar Campos Silva Wagner Campos Otoni 《In vitro cellular & developmental biology. Plant》2012,48(1):67-72
In vitro propagation of neem (Azadirachta indica A. Juss.) may offer an efficient alternative to seed propagation of this species. For optimization of in vitro propagation, different basal salt formulations, growth regulators, and culture container sealants (polytetrafluoroethylene hydrophobic membranes [PTFE]) were evaluated. Nodal segments cultured on Murashige and Skoog (MS) medium showed the highest shoot formation per explant (1.67). Explants cultured in flasks containing MS medium with 0.5 mg L−1 benzyladenine, 0.5 mg L−1 kinetin, and 0.05 mg L−1 naphthaleneacetic acid, and sealed with two PTFE membranes, produced the highest number of shoots (4.04). In contrast, explants cultured in flasks without membranes showed leaf chlorosis and senescence. For plant recovery, regenerants were acclimatized in a substrate of coconut fiber and eucalyptus bark (1:1) and showed 80% survival. Our results indicated that the use of flasks with vents was beneficial for in vitro propagation of this important plant. 相似文献
105.
106.
Willian Batista‐Silva David B. Medeiros Accio Rodrigues‐Salvador Danilo M. Daloso Rebeca P. Omena‐Garcia Franciele Santos Oliveira Lilian Ellen Pino Lzaro Eustquio Pereira Peres Adriano Nunes‐Nesi Alisdair R. Fernie Agustín Zsgn Wagner L. Araújo 《Plant, cell & environment》2019,42(2):448-465
Auxin modulates a range of plant developmental processes including embryogenesis, organogenesis, and shoot and root development. Recent studies have shown that plant hormones also strongly influence metabolic networks, which results in altered growth phenotypes. Modulating auxin signalling pathways may therefore provide an opportunity to alter crop performance. Here, we performed a detailed physiological and metabolic characterization of tomato (Solanum lycopersicum) mutants with either increased (entire) or reduced (diageotropica—dgt) auxin signalling to investigate the consequences of altered auxin signalling on photosynthesis, water use, and primary metabolism. We show that reduced auxin sensitivity in dgt led to anatomical and physiological modifications, including altered stomatal distribution along the leaf blade and reduced stomatal conductance, resulting in clear reductions in both photosynthesis and water loss in detached leaves. By contrast, plants with higher auxin sensitivity (entire) increased the photosynthetic capacity, as deduced by higher Vcmax and Jmax coupled with reduced stomatal limitation. Remarkably, our results demonstrate that auxin‐sensitive mutants (dgt) are characterized by impairments in the usage of starch that led to lower growth, most likely associated with decreased respiration. Collectively, our findings suggest that mutations in different components of the auxin signalling pathway specifically modulate photosynthetic and respiratory processes. 相似文献
107.
Nouaille S Ribeiro LA Miyoshi A Pontes D Le Loir Y Oliveira SC Langella P Azevedo V 《Genetics and molecular research : GMR》2003,2(1):102-111
Lactic acid bacteria (LAB), widely used in the food industry, are present in the intestine of most animals, including humans. The potential use of these bacteria as live vehicles for the production and delivery of heterologous proteins of vaccinal, medical or technological interest has therefore been extensively investigated. Lactococcus lactis, a LAB species, is a potential candidate for the production of biologically useful proteins. Several delivery systems have been developed to target heterologous proteins to a specific cell location (i.e., cytoplasm, cell wall or extracellular medium). A promising application of L. lactis is its use as an antigen delivery vehicle, for the development of live mucosal vaccines. The expression of heterologous proteins and antigens as well as the various delivery systems developed in L. lactis, and its use as an oral vaccine carrier are discussed. 相似文献
108.
Milhomem SS Crampton WG Pieczarka JC Shetka GH Silva DS Nagamachi CY 《Journal of fish biology》2012,80(4):802-815
Gymnotus capanema n. sp. is described on the basis of cytogenetic, morphometric, meristic and osteological data from nine specimens (one male and eight females) from the municipality of Capanema, Pará, in the eastern Amazon of Brazil. Later, three additional specimens were found in museums and regarded as nontypes (not cytogenetically analysed). Gymnotus capanema, which occurs in sympatry with Gymnotus cf. carapo cytotype 2n = 42 (30m/sm + 12st/a) exhibits a novel karyotype for the genus, with 2n = 34 (20m/sm + 14st/a). Gymnotus capanema can be unambiguously diagnosed from all congeners on the basis of a combination of characters from external anatomy, pigmentation and osteology. The constitutive heterochromatin, rich in adenine-thymine (A-T) base pairs [4',6 diamidino-2-phenylindole dihydrochloride (DAPI) positive], occurs in the centromeric region of all of the chromosomes, and in the pericentromeric and the entire short arm of some chromosomes. The nucleolar organizing region (NOR), stained by silver nitrate, chromomycin A(3) (CMA(3)) and 18S ribosomal (r)DNA fluorescence in situ hybridization (FISH), occurs in the short arm of pair 15. FISH, with telomeric probes did not show interstitial telomeric sequences (ITS), despite the reduced 2n in comparison to the karyotypes of other species of Gymnotus. The karyotype of G. capanema, with a reduced 2n, is strikingly different from all other previously studied congeners. 相似文献
109.
Milena Lima de Moraes Renata de Faria Barbosa Raquel Espírito Santo Flávia da Silva Santos Edgar Francisco Oliveira de Jesus Fátima Lúcia de Carvalho Sardinha Maria das Graças Tavares do Carmo 《Biological trace element research》2011,139(2):126-136
Adolescence is marked by intensive growth and development. When pregnancy occurs during this period of the mother’s growth,
there is an increase in her nutritional needs. The aim of this study was to determine the levels of calcium, iron, copper,
and zinc in maternal plasma, the placenta, and in the cord plasma of pregnant teenagers and adults. A total of 80 sets of
maternal plasma, placentas, and cord plasma (40 from teenagers and 40 from adults) were analyzed using synchrotron radiation
total reflection X-ray fluorescence. The levels of calcium, copper, and zinc in the maternal and cord plasma from teenagers
were not significantly different than those from adults. Iron levels in the teenagers maternal and cord plasma were higher
than in the adults. All of the minerals analyzed were present at higher levels in the placentas from adults than those from
teenagers. However, the low quantities of placental calcium, iron, copper, and zinc in the teenagers do not compromise the
levels of these minerals in the cord plasma. Future research regarding the placental transport of these minerals is recommended
to investigate the efficiency of mechanisms of transfer of these minerals in pregnant teenagers. 相似文献
110.
Priscila da Silva Delabona Deise Juliana Lima Diogo Robl Sarita Cândida Rabelo Cristiane Sanchez Farinas José Geraldo da Cruz Pradella 《Journal of industrial microbiology & biotechnology》2016,43(5):617-626
The use of glycerol obtained as an intermediate of the biodiesel manufacturing process as carbon source for microbial growth is a potential alternative strategy for the production of enzymes and other high-value bioproducts. This work evaluates the production of cellulase enzymes using glycerol for high cell density growth of Trichoderma harzianum followed by induction with a cellulosic material. Firstly, the influence of the carbon source used in the pre-culture step was investigated in terms of total protein secretion and fungal morphology. Enzymatic productivity was then determined for cultivation strategies using different types and concentrations of carbon source, as well as different feeding procedures (batch and fed-batch). The best strategy for cellulase production was then further studied on a larger scale using a stirred tank bioreactor. The proposed strategy for cellulase production, using glycerol to achieve high cell density growth followed by induction with pretreated sugarcane bagasse, achieved enzymatic activities up to 2.27 ± 0.37 FPU/mL, 106.40 ± 8.87 IU/mL, and 9.04 ± 0.39 IU/mL of cellulase, xylanase, and β-glucosidase, respectively. These values were 2 times higher when compared to the control experiments using glucose instead of glycerol. This novel strategy proved to be a promising approach for improving cellulolytic enzymes production, and could potentially contribute to adding value to biomass within the biofuels sector. 相似文献