全文获取类型
收费全文 | 17215篇 |
免费 | 1420篇 |
国内免费 | 8篇 |
专业分类
18643篇 |
出版年
2024年 | 21篇 |
2023年 | 132篇 |
2022年 | 311篇 |
2021年 | 534篇 |
2020年 | 311篇 |
2019年 | 401篇 |
2018年 | 462篇 |
2017年 | 352篇 |
2016年 | 665篇 |
2015年 | 1079篇 |
2014年 | 1162篇 |
2013年 | 1347篇 |
2012年 | 1632篇 |
2011年 | 1461篇 |
2010年 | 931篇 |
2009年 | 773篇 |
2008年 | 1021篇 |
2007年 | 997篇 |
2006年 | 888篇 |
2005年 | 809篇 |
2004年 | 773篇 |
2003年 | 617篇 |
2002年 | 617篇 |
2001年 | 105篇 |
2000年 | 90篇 |
1999年 | 110篇 |
1998年 | 125篇 |
1997年 | 96篇 |
1996年 | 90篇 |
1995年 | 65篇 |
1994年 | 60篇 |
1993年 | 49篇 |
1992年 | 48篇 |
1991年 | 38篇 |
1990年 | 37篇 |
1989年 | 48篇 |
1988年 | 38篇 |
1987年 | 24篇 |
1986年 | 20篇 |
1985年 | 28篇 |
1984年 | 30篇 |
1983年 | 22篇 |
1982年 | 19篇 |
1981年 | 18篇 |
1980年 | 21篇 |
1979年 | 19篇 |
1978年 | 13篇 |
1976年 | 17篇 |
1974年 | 13篇 |
1968年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
To better understand the outcomes of companion animal adoptions, Bardsley & Neidhart Inc. conducted a series of 3 surveys over a 1-year period with dog and cat owners who had adopted their pet through either a (a) Luv-A-Pet location, (b) Adopt-a-thon, or (c) traditional shelter. This article suggests opportunities to improve owners' perceptions of their pets and the adoption process through (a) providing more information before adoption about pet health and behaviors, (b) providing counseling to potential adopters to place pets appropriately, and (c) educating adopters to promote companion animal health and retention. Results demonstrate that the pet's relationship to the family unit, such as where the pet sleeps and how much time is spent with the pet, is related to the amount of veterinary care the companion animal receives, and to long-term retention. Satisfaction and retention are attributed to the pet's personality, compatibility, and behavior, rather than demographic differences among adopters or between adoption settings. The age of the companion animal at adoption, the intended recipient, and presence of children in the home also play a role. Health problems were an issue initially for half of all adopted pets, but most were resolved within 12 months. Roughly one fourth of adopters who no longer have their companion animal said their pet died. Characteristics of pets that died support the contention that spaying and neutering profoundly affects a companion animal's life span. Although retention is similar for dogs and cats, mortality is higher among cats in the first year after adoption. 相似文献
102.
Valentinuzzi Fabio Venuti Silvia Pii Youry Marroni Fabio Cesco Stefano Hartmann Felix Mimmo Tanja Morgante Michele Pinton Roberto Tomasi Nicola Zanin Laura 《Plant molecular biology》2019,101(1-2):129-148
Plant Molecular Biology - Iron and phosphorus are abundant elements in soils but poorly available for plant nutrition. The availability of these two nutrients represents a major constraint for... 相似文献
103.
Juaristi Inés Contreras Laura González-Sánchez Paloma Pérez-Liébana Irene González-Moreno Luis Pardo Beatriz del Arco Araceli Satrústegui Jorgina 《Neurochemical research》2019,44(10):2385-2391
Neurochemical Research - The brain uses mainly glucose as fuel with an index of glucose to oxygen utilization close to 6, the maximal index if all glucose was completely oxidized. However, this... 相似文献
104.
Deborah F. Tate Leslie Lytle Kristen Polzien Molly Diamond Kelsey R. Leonard John M. Jakicic Karen C. Johnson Christine M. Olson Kevin Patrick Laura P. Svetkey Rena R. Wing Pao‐Hwa Lin Mathilda Coday Melissa N. Laska Gina Merchant Sara J. Czaja Richard Schulz Steven H. Belle 《Obesity (Silver Spring, Md.)》2019,27(7):1085-1098
105.
Pineda Alfonso Iatskiu Patrícia Jati Susicley Paula Aline C. M. Zanco Bárbara F. Bonecker Claudia C. Moresco Geovani A. Ortega Laura A. Souza Yasmin R. Rodrigues Luzia C. 《Hydrobiologia》2020,847(18):3857-3875
Hydrobiologia - We analyzed the effect of damming on the temporal patterns of the composition and richness of phytoplankton Reynolds functional groups (RFG) from a subtropical floodplain, together... 相似文献
106.
107.
Amici M Cecarini V Pettinari A Bonfili L Angeletti M Barocci S Biagetti M Fioretti E Eleuteri AM 《Biological chemistry》2007,388(1):107-117
Aflatoxins (AF) are contaminants of improperly stored foods; they are potent genotoxic and carcinogenic compounds, exerting their effects through damage to DNA. They can also induce mutations that increase oxidative damage. The goal of this study was to evaluate the possibility that a third mechanism could be involved in the carcinogenic action of aflatoxins, namely, direct binding to key enzymes involved in the regulatory pathways of the cell cycle, thereby modulating enzyme functionality. The 20S constitutive and immunoproteasome peptidase and proteolytic activities were assayed in the presence of aflatoxins B1, G1 and M1. All three toxins activated multiple peptidase activities of the proteasome. Aflatoxin (AF) M1 was the most potent activator of proteasome activity, while the constitutive 20S proteasome was specifically stimulated by AFG1. Furthermore, the effects of AFB1 on cultured hepatoma cells were investigated and the various proteasomal activities determined with cell lysates were differently affected. Taking into account the key role of the proteasome in cellular defense against oxidative stress, the carbonyl group content and the activities of antioxidant enzymes in cell lysates were analyzed. The proapoptotic effect of AFB1 was also investigated by measuring caspase-3 activity and cellular levels of p27 and IkappaBalpha. 相似文献
108.
Gram-negative bacteria most often use N-acyl homoserine lactones (AHLs) as intercellular quorum-sensing signal molecules. In this study, it was demonstrated that rice plants contain AHL mimic molecules that are very sensitive to the highly specific AiiA lactonase enzyme and can activate three different AHL bacterial biosensors, indicating that the compounds have a homoserine lactone structure and could be AHLs. The possible source and biological significance of this finding are discussed. 相似文献
109.
Susan Singer John Sollinger Sonja Maki Jason Fishbach Brad Short Catherine Reinke Jennifer Fick Laura Cox Andrew McCall Heidi Mullen 《The Botanical review》1999,65(4):385-410
We are characterizing a suiteof Pisum sativum mutants that alter inflorescence architecture to construct a model for the genetic regulation of inflorescence development
in a plant with a compound raceme. Such a model, when compared with those created forAntirrhinum majus andArabidopsis thaliana, both of which have simple racemes, should provide insight into the evolution of the development of inflorescence architecture.
The highly conserved nature of cloned genes that regulate reproductive development in plants and the morphological similarities
among our mutants and those identified inA. majus andA. thaliana enhance the probability that a developmental genetics approach will be fruitful. Here we describe sixP. sativum mutants that affect morphologically and architecturally distinct aspects of the inflorescence, and we analyze interactions
among these genes. Both vegetative and inflorescence growth of the primary axis is affected byUNIFOLIA TA, which is necessary for the function ofDETERMINATE (DET).DET maintains indeterminacy in the first-order axis. In its absence, the meristem differentiates as a stub covered with epidermal
hairs.DET interacts withVEGETATIVE1 (VEG1).VEG1 appears essential for second-order inflorescence (I2) development.veg1 mutants fail to flower or differentiate the I2 meristem into a rudimentary stub,det veg1 double mutants produce true terminal flowers with no stubs, indicating that two genes must be eliminated for terminal flower
formation inP. sativum, whereas elimination of a single gene accomplishes this inA. thaliana andA. majus. NEPTUNE also affects I2 development by limiting to two the number of flowers produced prior to stub formation. Its role is independent ofDET, as indicated by the additive nature of the double mutantdet nep. UNI, BROC, and PIM all play roles in assigning floral meristem identity to the third-order branch.pim mutants continue to produce inflorescence branches, resulting in a highly complex architecture and aberrant flowers.uni mutants initiate a whorl of sepals, but floral organogenesis is aberrant beyond that developmental point, and the double
mutantuni pim lacks identifiable floral organs. A wild-type phenotype is observed inbroc plants, butbroc enhancesthe pim phenotype in the double mutant, producing inflorescences that resemble broccoli. Collectively these genes ensure that only
the third-order meristem, not higher- or lower-order meristems, generates floral organs, thus precisely regulating the overall
architecture of the plant.
Gene symbols used in this article: For clarity a common symbolization is used for genes of all species discussed in this article.
Genes are symbolized with italicized capital letters. Mutant alleles are represented by lowercase, italicized letters. In
both cases, the number immediately following the gene symbol differentiates among genes with the same symbol. If there are
multiple alleles, a hyphen followed by a number is used to distinguish alleles. Protein products are represented by capital
letters without italics. 相似文献
110.
Huw S. Groucutt Michael D. Petraglia Geoff Bailey Eleanor M. L. Scerri Ash Parton Laine Clark‐Balzan Richard P. Jennings Laura Lewis James Blinkhorn Nick A. Drake Paul S. Breeze Robyn H. Inglis Maud H. Devès Matthew Meredith‐Williams Nicole Boivin Mark G. Thomas Aylwyn Scally 《Evolutionary anthropology》2015,24(4):149-164
Current fossil, genetic, and archeological data indicate that Homo sapiens originated in Africa in the late Middle Pleistocene. By the end of the Late Pleistocene, our species was distributed across every continent except Antarctica, setting the foundations for the subsequent demographic and cultural changes of the Holocene. The intervening processes remain intensely debated and a key theme in hominin evolutionary studies. We review archeological, fossil, environmental, and genetic data to evaluate the current state of knowledge on the dispersal of Homo sapiens out of Africa. The emerging picture of the dispersal process suggests dynamic behavioral variability, complex interactions between populations, and an intricate genetic and cultural legacy. This evolutionary and historical complexity challenges simple narratives and suggests that hybrid models and the testing of explicit hypotheses are required to understand the expansion of Homo sapiens into Eurasia. 相似文献